Introduction

1,3-Diaryl-2-propen-1-ones (chalcones) are one of the most important classes of natural products, and are widespread in the plant kingdom. Chalcones (natural or synthetic) possess a broad spectrum of biological activities including anti-inflammatory (Ballesteros et al.,1995), antifungal (Nowakowska, 2007), antioxidant (Mukherjee et al., 2001), antimalarial (Wu et al., 2002), antituberculosis (Sivakumar et al., 2007), analgesic (Viana et al., 2003), antitumor (Shibata, 1994), anticancer (Wattenberg et al., 1994), antiviral (Trivedi et al., 2007), anti-AIDS (Wu et al., 2003) and antileishmanial agents (Boeck et al., 2006).

Pyrazoline derivatives of chalcones have been reported to possess a widespread range of biological activities like antibacterial (Nauduri and Reddy, 1998), antifungal (Azarifar and Shaebanzadeh, 2002), antidepressant (Bilgin et al., 1993), antitumor (Taylor and Patel, 1992), antimicrobial (Ramalingham et al., 1977), anti-inflammatory, molluscicidal activity (Barsoum et al., 2006), antiamoebic (Budakoti et al., 2006), anticonvulsant activities (Ozdemir et al., 2007). One of the most famous pyrazole-based drugs used as a non-steroidal anti-inflammatory drug (NSAID) is celecoxib (Fig. 1) (Rezende, et al., 2010). Considerable attention has been focused on the pyrazoline family in the last two decades. Among various pyrazoline derivatives, 2-pyrazolines seem to be the most frequently studied pyrazoline-type compounds (Lévai, 2005). After the pioneering work by Fischer and Knövenagel in the late nineteenth century, the reaction of α,β-unsaturated aldehydes and ketones with hydrazines became one of the most popular methods for the preparation of 2-pyrazolines (Lévai et al., 2004).

Fig. 1
figure 1

Structures of a quinoline and a pyrazole-based drugs

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Quinolines and their derivatives, which represent a major class of heterocycles (Meth-Cohn and Narine, 1978) and are widely found in natural products (Michael 2003, 2004) and drugs (Alhaider et al., 1985; Campbell et al., 1988; Du, 2003), exhibit significant role in medicinal chemistry. Several quinoline derivatives have been reported to exhibit bactericidal (Awad et al., 1991), antimalarial (Ginsburg et al., 1999), antiallergenic (Althuis et al., 1980) and anti-inflammatory (Dillard et al., 1973) properties. Some of the famous antimalarial drugs, containing quinoline ring system; available in the market are plasmoquine (Manske and Kulka, 1953), primaquine and chloroquine (Singh et al., 1978). Many quinoline derivatives are found to possess anticancer and antitumor activities (Loaiza et al., 2004). Among the quinolines, 2-chloro-3-formylquinolines find an important place in synthetic organic chemistry, as these are key intermediates for further β-annelation of a wide variety of ring systems and for the inter-conversions of many functional groups (Meth-Cohn, 1993).

In this study, the 2-chloro-7/8-methyl-3-formylquinoline nucleus and chalcone functionality have been incorporated in a single molecule (1a–k and 2a–k). Then each of the prepared chalcones was refluxed with hydrazine hydrate in ethanol to yield twenty-two novel 2-pyrazolines (3a–k and 4a–k) based on quinolyl-thienyl ring systems. Finally, all the title compounds were tested for their antileishmanial activities.

Results and discussion

Chemistry

The two precursors, 2-chloro-3-formyl-7- and 8-methyl-quinoline were prepared by reported method (Meth-Cohn et al., 1981). Synthesis of the chalconess (1a–k and 2a–k) was based on Claisen-Schmidt condensation (Li et al., 1995). For this purpose, the prepared formyl quinolines were condensed with commercially available acetyl thiophenes (Table 1), in the presence of sodium hydroxide. Finally, chalcones thus prepared, on cyclization with hydrazine hydrate, gave the corresponding 2-pyrazoline derivatives (3a–k and 4a–k) in a reasonably good yield (Scheme 1).

Table 1 Aryl moiety (Ar) in chalcones (1a–k) and (2a–k)
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Scheme 1
scheme 1

Reaction protocol for the synthesis of 2-pyralozine derivatives (3a–k) and (4a–k) (i) AcOH, H3PO4, reflux, 4–6 h, (ii) POCl3, DMF, 80°C, (iii) a–k, NaOH, rt, 2 h, (iv) Hydrazine, EtOH, reflux

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Spectral data (IR, 1H-NMR and MS) of all the newly synthesized compounds were found in good agreement with the proposed structures. IR spectra of the compounds 1a–k and 2a–k showed an absorption band at 1650 cm−1, typical of the stretching vibrations of chalcone moiety. No peaks were found due to starting material aldehydic functionality as impurity. In the 1H-NMR spectra of the chalcones (1a–k except 1e, 1f and 1i) and (2a–k except 2e, 2f and 2i), two very sharp doublets around δ 7.40 ppm for Hα and δ 8.20 ppm for Hβ, with J-value 15–16 Hz for the trans chalcones were exhibited. Interestingly, in chalcones 1e and 2e, Hα and Hβ showed a doublet in the upfield at δ 7.33–7.32 and 8.10–8.08 ppm, respectively. This may be attributed to an additional +I effect induced by CH3 group present in the close vicinity. Similarly, in chalcones (1f, 1i, 2f and 2i), Hα revealed a doublet relatively in the downfield at δ 7.82–7.81 ppm. This may be attributed to an additional −I effect due to Cl/Br in the vicinity. The molecular ion observed in the mass spectra for all the chalcones confirmed their molecular masses. The base peak, in the mass spectra of most of the chalcones, was obtained possibly by the cleavage of HC–CO bond in the chalcone moiety. While in bromo- and iodo-substituted chalcones (1i–1k and 2i–2k), the base peak is due to the cleavage of two bonds, i.e. CO—thiophenyl and Br/I—thiophenyl bonds. The E-configuration was confirmed by X-ray structure of two similar structured chalcones which were already reported (Rizvi et al., 2008).

Similarly, in case of 2-pyrazolines (3a–k and 4a–k), IR spectra of all the compounds did not show absorbance at 1650 cm−1 which confirmed the absence of the chalcone moiety. A new peak with absorption band at 3280 cm−1 was revealed due to NH of 2-pyrazoline ring. 1H-NMR spectra of the pyrazolines (3a–k and 4a–k) ascertained the presence of two doublets of doublet signals due to CH2 protons Hα (upfield H of CH2) at δ 2.82–3.21 ppm region and Hβ (downfield H of CH2) at δ 3.64–4.10 ppm, respectively. The CH proton appeared as a triplet at δ 5.28–5.40 ppm region. The molecular ion M+, observed in the mass spectra for all the pyrazolines confirmed their molecular masses. The base peak, in almost all the mass spectra (except for 3f), was exhibited by M+ itself.

Antileishmanial activity

According to the results obtained, structure–activity relationship among the two series of chalcones (1a–k and 2a–k) may be explained in terms of stereo- and electronic and/or steric properties (see Fig. 2).

Fig. 2
figure 2

Proposed stereo-, electronic and/or steric properties (i) electronic effect (attractive forces), (ii) steric effect; (iii) electronic effect (dipolar repulsive forces)

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For example, the unsubstituted thiophenyl derivatives (1a and 2a) have prominent difference in antileishmanial activities, i.e. 2a is more active than 1a (IC50 = 0.88 ± 0.20 μg/ml for 1a and IC50 = 0.61 ± 0.81 μg/ml for 2a), while the activity decreased considerably by the introduction of CH3 group at position 3 of thiophenyl ring (1b and 2b; Table 2) perhaps due to steric effect, whereas, the activity is relatively increased on moving the methyl substituent to position 4 (1c and 2c) or 5 (1d and 2d) impairing the steric effect. Conversely, replacing the methyl group by chloro group at position 3 of thiophenyl ring (1f and 2f) results in enhanced activity. This may be attributed to the greater electronic effect of chloro group, while the steric effect of bromo group overweighs the electronic effect at position 3 of thiophenyl ring (1i and 2i). Moreover, substituting the halogen atoms (Cl, Br and I) at position 5 of thiophenyl ring (1g, 1j, 1k, 2g, 2j and 2k) deactivates these compounds due to the absence of electronic effect stereochemically. Similarly, 2,5-disubstituted methyl derivatives (1e and 2e) displayed more activity than their dichloro analogs (1h and 2h). This may be attributed to the possibility of existence of electronic effect which is due to the dipolar repulsive forces as shown in Fig. 2d by curved arrow (iii). While, there is no such electronic or steric effect in dimethyl derivatives (1e and 2e).

Table 2 Antileishmanial activity of series 1a–k, 2a–k, 3a–k and 4a–k (IC50 values)
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It is quite obvious from Table 2 that conversion of both series of chalcones (1a–k and 2a–k) to their corresponding 2-pyrazoline derivatives (3a–k and 4a–k) results in an overall decrease in the antileishmanial activity. This fact clearly indicates the significance of chalcone moiety towards antileishmanial activity in the titled compounds. In Fig. 2, this is proposed to be due to electronic effect shown by curved arrows, labelled as (i), which is vanished by the ring-closure at chalcones moiety.

Conclusion

It is evident from the above discussion that the chalcones (1a–k and 2a–k) exhibited more activity than their corresponding pyrazoline derivatives (3a–k and 4a–k). We divided the compounds into four categories for their antileishmanial activities and represrented in Table 3, i.e. IC50 = 0.59–0.56 μg/ml or below as significantly active, 0.69–0.60 μg/ml as good activity, 0.79–0.70 μg/ml as moderately active and 0.95–0.80 μg/ml as low activity. The compounds 1e, 1f, 2a, 2c, 2d, 2g, 2k and 4a were found potentially active antileishmanial agents.

Table 3 Proposed categories of antileishmanial agents
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Experimental

General

Melting points were taken on Gallenkamp melting point apparatus and remained uncorrected. IR spectra were recorded in KBr pellets on Perkin Elmer infrared spectrophotometer. 1H NMR spectra were performed in CDCl3 on Brücker/XWIN NMR (400 MHz) and TMS was used as internal standard (chemical shifts, δ in ppm) unless otherwise specified. Mass spectra were recorded on a Jeol MSRoute instrument. Thin layer chromatography (TLC) was performed with aluminium sheets-Silica gel 60 F254 purchased from Merck. Purification of synthesized compounds was made by recrystallization from appropriate solvents. Reagent grade chemiocals such as phosphoryl chloride, acetyl thiophenes, o-toluidine, m-toluidine, N,N-dimethylformamide and hydrazine hydrate (Aldrich and Alpha Aesar) were used as received. Elemental analyses were performed by C.S.I.C., Madrid Spain and were within ±0.4% of predicted values for all compounds.

General procedure for the preparation of (2E)-3-(2-chloro-7/8-methylquinolin-3-yl)-1-(Ary) prop-2-en-1-ones (1a–k) and (2a–k)

The two precursors, 7/8-methyl-substituted 2-chloro-3-formylquinolines were synthesized following literature method (Meth-Cohn et al., 1981). A mixture of formylquinoline (10 mmol) and an aromatic ketone (10 mmol) in methanol (50 ml) was stirred at room temperature, followed by dropwise addition of aq. NaOH (4 ml, 10%). The stirring was continued for 2 h and the reaction mixture was then kept at 0°C for 24 h. Subsequently, it was poured onto ice-cold water (200 ml). The precipitates were collected by filtration, washed with cold water followed by cold MeOH. The resulting chalcones were recrystallized from CHCl3 and dried in vacuo.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-thien-3-ylprop-2-en-1-one (1a)

Yield, 65%; colourless solid. mp 180–182°C. IR (KBr, cm−1): 1649 (C=O), 1594 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.57 (3H, s, Me), 7.39 (1H, dd, H4′, J = 5.1 Hz, 2.9 Hz), 7.42 (1H, dd, H5, J = 8.2 Hz, 1.2 Hz), 7.45 (1H, d, Hα, J = 15.7 Hz), 7.69 (1H, dd, H5′, J = 5.1 Hz, 1.0 Hz), 7.76 (1H, d, H6, J = 8.3 Hz), 7.79 (1H, s, H8), 8.19 (1H, d, Hβ, J = 15.6 Hz), 8.20 (1H, dd, H2′, J = 2.9 Hz, 1.0 Hz), 8.42 (1H, s, H4). MS (m/z): 313 (M+, 1.86%), 111 (M+–C12H9NCl, 100%). Anal. Calcd for C17H12ClNOS: C, 65.07; H, 3.85; N, 4.46. Found: C, 65.03; H, 3.76; N, 4.43.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(3-methylthien-2-yl) prop-2-en-1-one (1b)

Yield, 51%; pale yellow solid. mp 208–210°C. IR (KBr, cm−1): 1653 (C=O), 1594 (C=C), 1563 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56–2.66 (s, 2× Me), 7.02 (1H, d, H4′, J = 4.9 Hz), 7.40 (1H, d, Hα, J = 15.4 Hz), 7.42 (1H, dd, H5, J = 8.2 Hz, 1.3 Hz), 7.49 (1H, d, H5′ J = 4.9 Hz), 7.77 (1H, d, H6, J = 8.6 Hz), 7.78 (1H, s, H8), 8.18 (1H, d, Hβ, J = 15.4 Hz), 8.40 (1H, s, H4). MS (m/z): 327 (M+, 10%), 125 (M+–C12H9NCl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.92; H, 4.25; N, 4.25.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(4-methylthien-2-yl)prop-2-en-1-one (1c)

Yield, 56%; yellow solid. mp 173–174°C. IR (KBr, cm−1): 1655 (C=O), 1594 (C=C), 1564 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.33–2.56 (s, 2× Me), 7.31 (1H, s, H5′), 7.42 (1H, dd, H5, J = 8.2 Hz, 1.3 Hz), 7.44 (1H, d, Hα, J = 15.5 Hz), 7.71 (1H, s, H3′), 7.76 (1H, d, H6, J = 8.3 Hz), 7.79 (1H, s, H8), 8.21 (1H, d, Hβ, J = 15.6 Hz), 8.42 (1H, s, H4). MS (m/z): 327 (M+, %), 125 (M+–C12H9NCl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.85; H, 4.24; N, 4.23.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(5-methylthien-2-yl)prop-2-en-1-one (1d)

Yield, 52%; pale yellow solid. mp 173–175°C. IR (KBr, cm−1): 1652 (C=O), 1595 (C=C), 1563 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56–2.57 (s, 2× Me), 6.86 (1H, d, H4′, J = 3.3 Hz), 7.42 (1H, d, Hα, J = 15.6 Hz), 7.43 (1H, dd, H5, J = 8.2 Hz, 1.2 Hz), 7.71 (1H, d, H3′, J = 3.7 Hz), 7.75 (1H, d, H6, J = 8.3 Hz), 7.78 (1H, s, H8), 8.18 (1H, d, Hβ, J = 15.6 Hz), 8.40 (1H, s, H4). MS (m/z): 327 (M+, 3.61%), 125 (M+–C12H9NCl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.89; H, 4.26; N, 4.25.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(2,5-dimethylthien-3-yl)prop-2-en-1-one (1e)

Yield, 70%; yellow solid. mp 183–185°C. IR (KBr, cm−1): 1648 (C=O), 1590 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.44–2.72 (s, 3× Me), 7.10 (1H, s, H4′), 7.32 (1H, d, Hα, J = 15.7 Hz), 7.41 (1H, dd, H5, J = 8.4 Hz, 1.2 Hz), 7.74 (1H, d, H6, J = 8.3 Hz), 7.78 (1H, s, H8), 8.08 (1H, d, Hβ, J = 15.7 Hz), 8.37 (1H, s, H4). MS (m/z): 341 (M+, 10.31%), 306 (M+–Cl, 100%). Anal. Calcd for C19H16ClNOS: C, 66.75; H, 4.72; N, 4.10. Found: C, 66.65; H, 4.68; N, 4.08.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(3-chlorothien-2-yl)prop-2-en-1-one (1f)

Yield, 66%; yellow solid. mp 160–162°C. IR (KBr, cm−1): 1650 (C=O), 1591 (C=C), 1569 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56 (3H, s, Me), 7.07 (1H, d, H4′, J = 5.2 Hz), 7.28 (1H, dd, H5, J = 8.3 Hz, 1.1 Hz), 7.60 (1H, d, H5′, J = 5.2 Hz), 7.77 (1H, d, H6, J = 8.6 Hz), 7.82 (1H, d, Hα, J = 15.5 Hz), 7.96 (1H, s, H8), 8.23 (1H, d, Hβ, J = 15.5 Hz), 8.42 (1H, s, H4). MS (m/z): 347 (M+, 1.8%), 145 (M+–C12H9NCl, 100%). Anal. Calcd. for C17H11Cl2NOS: C, 58.63; H, 3.18; N, 4.02. Found: C, 58.53; H, 3.16; N, 3.97.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(5-chlorothien-2-yl)prop-2-en-1-one (1g)

Yield, 80%; pale yellow solid. mp 170–171°C. IR (KBr, cm−1): 1656 (C=O), 1598 (C=C), 1570 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52 (3H, s, Me), 6.92 (1H, d, H4′, J = 4.1 Hz), 7.35 (1H, dd, H5, J = 8.3 Hz, 1.2 Hz), 7.39 (1H, d, Hα, J = 15.6 Hz), 7.57 (1H, d, H3′, J = 4.1 Hz), 7.64 (1H, d, H6, J = 8.3 Hz), 7.72 (1H, s, H8), 8.20 (1H, d, Hβ, J = 15.6 Hz), 8.39 (1H, s, H4). MS (m/z): 347 (M+, 2.41%), 145 (M+–C12H9NCl, 100%). Anal. Calcd for C17H11Cl2NOS: C, 58.63; H, 3.18; N, 4.02. Found: C, 58.57; H, 3.14; N, 3.96.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(2,5-dichlorothien-3-yl)prop-2-en-1-one (1h)

Yield, 63%; off-white solid. mp 163°C. IR (KBr, cm−1): 1662 (C=O), 1596 (C=C), 1572 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56 (3H, s, Me), 7.23 (1H, s, H4′), 7.42 (1H, dd, H5, J = 8.3 Hz, 1.0 Hz), 7.45 (1H, d, Hα, J = 15.7 Hz), 7.76 (1H, d, H6, J = 8.3 Hz), 7.79 (1H, s, H8), 8.15 (1H, d, Hβ, J = 15.7 Hz), 8.39 (1H, s, H4). MS (m/z): 383 (M+, 1.7%), 346 (M+–Cl, 100%). Anal. Calcd for C17H10Cl3NOS: C, 53.35; H, 2.63; N, 3.66. Found: C, 53.26; H, 2.58; N, 3.67.

(2E)-1-(3-Bromothien-2-yl)-3-(2-chloro-7-methylquinolin-3-yl)prop-2-en-1-one (1i)

Yield, 79%; yellow solid. mp 164–165°C. IR (KBr, cm−1): 1652 (C=O), 1592 (C=C), 1568 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.57 (3H, s, Me), 7.16 (1H, d, H4′, J = 5.16 Hz), 7.42 (1H, dd, H5, J = 8.3 Hz, 1.3 Hz), 7.58 (1H, d, H5′, J = 5.2 Hz), 7.78 (1H, d, H6, J = 8.6 Hz), 7.82 (1H, d, Hα, J = 15.6 Hz), 7.79 (1H, s, H8), 8.23 (1H, d, Hβ, J = 15.5 Hz), 8.43 (1H, s, H4). MS (m/z): 393 (M+, 1.5%), 82 (M+–C13H9NOClBr, 100%). Anal. Calcd for C17H11BrClNOS: C, 51.99; H, 2.82; N, 3.57. Found: C, 51.94; H, 2.76; N, 3.56.

(2E)-1-(5-Bromothien-2-yl)-3-(2-chloro-7-methylquinolin-3-yl)prop-2-en-1-one (1j)

Yield, 75%; yellow solid. mp 162–164°C. IR (KBr, cm−1): 1653 (C=O), 1588 (C=C), 1566 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56 (3H, s, Me), 7.16 (1H, d, H4′, J = 4.0 Hz), 7.38 (1H, d, Hα, J = 15.6 Hz), 7.42 (1H, dd, H5, J = 8.3 Hz, 1.0 Hz), 7.63 (1H, d, H3′, J = 4.0 Hz), 7.76 (1H, d, H6, J = 8.3 Hz),7.79 (1H, s, H8), 8.21 (1H, d, Hβ, J = 15.6 Hz), 8.40 (1H, s, H4). MS (m/z): 393 (M+, 1.5%), 82 (M+–C13H9NOClBr, 100%). Anal. Calcd for C17H11BrClNOS: C, 51.99; H, 2.82; N, 3.57. Found: C, 51.95; H, 2.79; N, 3.56.

(2E)-3-(2-Chloro-7-methylquinolin-3-yl)-1-(5-iodothien-2-yl)prop-2-en-1-one (1k)

Yield, 90%; deep yellow solid. mp 164–165°C. IR (KBr, cm−1): 1650 (C=O), 1596 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.56 (3H, s, Me), 7.36 (1H, d, H4′, J = 4.0 Hz), 7.37 (1H, d, Hα, J = 15.5 Hz), 7.42 (1H, dd, H5, J = 8.4 Hz, 1.2 Hz), 7.50 (1H, d, H3′, J = 4.0 Hz), 7.76 (1H, d, H6, J = 8.3 Hz), 7.79 (1H, s, H8), 8.21 (1H, d, Hβ, J = 15.6 Hz), 8.40 (1H, s, H4). MS (m/z): 439 (M+, 1.5%), 82 (M+–C13H9NOICl, 100%). Anal. Calcd for C17H11ClINOS: C, 46.44; H, 2.52; N, 3.19. Found: C, 46.44; H, 2.43; N, 3.18.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-thien-3-ylprop-2-en-1-one (2a)

Yield, 60%; pale yellow solid. mp 128–130°C. IR (KBr, cm−1): 1649 (C=O), 1591 (C=C), 1561 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.39 (1H, dd, H4′, J = 5.1 Hz, 2.9 Hz), 7.46 (1H, d, Hα, J = 15.6 Hz), 7.47 (1H, t, H6, J = 7.6 Hz), 7.60 (1H, d, H7, J = 7.0 Hz), 7.69 (1H, d, H5′, J = 4.7 Hz, 1.1 Hz), 7.70 (1H, d, H5, J = 6.7 Hz), 8.20 (1H, d, Hβ, J = 15.7 Hz), 8.20 (1H, dd, H2′, J = 2.8 Hz, 1.1 Hz), 8.42 (1H, s, H4). MS (m/z): 313 (M+, 1.9%), 111 (M+–C12H9NCl, 100%). Anal. Calcd for C17H12ClNOS: C, 65.07; H, 3.85; N, 4.46. Found: C, 65.04; H, 3.78; N, 4.44.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(3-methylthien-2-yl)prop-2-en-1-one (2b)

Yield, 56%; yellow solid. mp 174–175°C. IR (KBr, cm−1): 1654 (C=O), 1594 (C=C), 1563 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.66–2.76 (s, 2× Me), 7.02 (1H, d, H4′, J = 4.9 Hz), 7.41 (1H, d, Hα, J = 15.4 Hz), 7.47 (1H, t, H6, J = 7.6 Hz), 7.49 (1H, d, H5′, J = 5.3 Hz), 7.59 (1H, d, H7, J = 7.0 Hz), 7.71 (1H, d, H5, J = 8.0 Hz), 8.20 (1H, d, Hβ, J = 15.4 Hz), 8.40 (1H, s, H4). MS (m/z): 327 (M+, 6.74%), 125 (M+–C12H9NCl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.90; H, 4.27; N, 4.27.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(4-methylthien-2-yl)prop-2-en-1-one (2c)

Yield, 49%; yellow solid. mp 146–147°C. IR (KBr, cm−1): 1655 (C=O), 1593 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.33–2.76 (s, 2× Me), 7.31 (1H, s, H5′), 7.46 (1H, d, Hα, J = 15.5 Hz), 7.47 (1H, t, H6, J = 7.6 Hz), 7.60 (1H, d, H7, J = 7.0 Hz), 7.70 (1H, d, H5, J = 7.0 Hz), 7.71 (1H, s, H3′), 8.23 (1H, d, Hβ, J = 15.6 Hz), 8.42 (1H, s, H4). MS (m/z): 327 (M+, 5.02%), 292 (M+–Cl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.85; H, 4.23; N, 4.22.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(5-methylthien-2-yl)prop-2-en-1-one (2d)

Yield, 55%; yellow solid. mp 180–181°C. IR (KBr, cm−1): 1652 (C=O), 1596 (C=C), 1563 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.57–2.75 (s, 2× Me), 6.86 (1H, d, H4′, J = 3.1 Hz), 7.43 (1H, d, Hα, J = 15.6 Hz), 7.46 (1H, t, H6, J = 7.7 Hz), 7.59 (1H, d, H7, J = 7.0 Hz), 7.69 (1H, d, H5, J = 8.2 Hz), 7.72 (1H, d, H3′, J = 3.8 Hz), 8.19 (1H, d, Hβ, J = 15.6 Hz), 8.40 (1H, s, H4). MS (m/z): 327 (M+, 5.56%), 125 (M+–C12H9NCl, 100%). Anal. Calcd for C18H14ClNOS: C, 65.95; H, 4.30; N, 4.27. Found: C, 65.86; H, 4.25; N, 4.25.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(2,5-dimethylthien-3-yl)prop-2-en-1-one (2e)

Yield, 67%; yellow solid. mp 138–140°C. IR (KBr, cm−1): 1648 (C=O), 1585 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.44–2.75 (s, 3× Me), 7.10 (1H, s, H4′), 7.33 (1H, d, Hα, J = 15.7 Hz), 7.46 (1H, t, H6, J = 7.7 Hz), 7.59 (1H, d, H7, J = 7.0 Hz), 7.68 (1H, d, H5, J = 8.1 Hz), 8.10 (1H, d, Hβ, J = 15.7 Hz), 8.37 (1H, s, H4). MS (m/z): 341 (M+, 7.71%), 139 (M+–C12H9NCl, 100%). Anal. Calcd for C19H16ClNOS: C, 66.75; H, 4.72; N, 4.10. Found: C, 66.66; H, 4.62; N, 4.02.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(3-chlorothien-2-yl)prop-2-en-1-one (2f)

Yield, 73%; yellow solid. mp 162–163°C. IR (KBr, cm−1): 1650 (C=O), 1592 (C=C), 1570 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.07 (1H, d, H4′, J = 5.3 Hz), 7.47 (1H, t, H6, J = 7.7 Hz), 7.59 (1H, d, H7, J = 7.0 Hz), 7.60 (1H, d, H5′, J = 5.3 Hz), 7.71 (1H, d, H5, J = 8.1 Hz), 7.82 (1H, d, Hα, J = 15.5 Hz), 8.24 (1H, d, Hβ, J = 15.6 Hz), 8.42 (1H, s, H4). MS (m/z): 347 (M+, 1.18%), 145 (M+–C12H9NCl, 100%). Anal. Calcd. for C17H11Cl2NOS: C, 58.63; H, 3.18; N, 4.02. Found: C, 58.59; H, 3.12; N, 3.98.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(5-chlorothien-2-yl) prop-2-en-1-one (2g)

Yield, 85%; pale yellow solid. mp 166–168°C. IR (KBr, cm−1): 1656 (C=O), 1598 (C=C), 1572 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.02 (1H, d, H4′, J = 4.0 Hz), 7.39 (1H, d, Hα, J = 15.5 Hz), 7.48 (1H, t, H6, J = 7.6 Hz), 7.61 (1H, d, H7, J = 7.0 Hz), 7.68 (1H, d, H3′, J = 4.2 Hz), 7.70 (1H, d, H5, J = 8.1 Hz), 8.23 (1H, d, Hβ, J = 15.6 Hz), 8.41 (1H, s, H4). MS (m/z): 347 (M+–Cl, 1.24%), 145 (M+–C12H9NCl, 100%). Anal. Calcd for C17H11Cl2NOS: C, 58.63; H, 3.18; N, 4.02. Found: C, 58.55; H, 3.13; N, 3.97.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(2,5-dichlorothien-3-yl)prop-2-en-1-one (2h)

Yield, 69%; colourless solid. mp 120–121°C. IR (KBr, cm−1): 1664 (C=O), 1596 (C=C), 1570 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.15 (1H, s, H4′), 7.45 (1H, d, Hα, J = 15.7 Hz), 7.47 (1H, t, H6, J = 7.7 Hz), 7.61 (1H, d, H7, J = 6.8 Hz), 7.70 (1H, d, H5, J = 8.1 Hz), 8.17 (1H, d, Hβ, J = 15.7 Hz), 8.39 (1H, s, H4). MS (m/z): 383 (M+, 1.8%), 179 (M+–C12H9NCl, 100%). Anal. Calcd for C17H10Cl3NOS: C, 53.35; H, 2.63; N, 3.66. Found: C, 53.24; H, 2.55; N, 3.60.

(2E)-1-(3-Bromothien-2-yl)-3-(2-chloro-8-methylquinolin-3-yl) prop-2-en-1-one (2i)

Yield, 86%; yellow solid. mp 210–212°C. IR (KBr, cm−1): 1652 (C=O), 1592 (C=C), 1568 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.16 (1H, d, H4′, J = 5.2 Hz), 7.47 (1H, t, H6, J = 7.6 Hz), 7.58 (1H, d, H5′, J = 5.2 Hz), 7.60 (1H, d, H7, J = 7.1 Hz), 7.71 (1H, d, H5, J = 8.0 Hz), 7.81 (1H, d, Hα, J = 15.6 Hz), 8.25 (1H, d, Hβ, J = 15.5 Hz), 8.44 (1H, s, H4). MS (m/z): 393 (M+, 1.0%), 82 (M+–C13H9NOClBr, 100%). Anal. Calcd. for C17H11BrClNOS: C, 51.99; H, 2.82; N, 3.57. Found: C, 51.98; H, 2.77; N, 3.59.

(2E)-1-(5-Bromothien-2-yl)-3-(2-chloro-8-methylquinolin-3-yl) prop-2-en-1-one (2j)

Yield, 71%; off-white solid. mp 204–206°C. IR (KBr, cm−1): 1653 (C=O), 1588 (C=C), 1566 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.17 (1H, d, H4′, J = 4.0 Hz), 7.39 (1H, d, Hα, J = 15.6 Hz), 7.48 (1H, t, H6, J = 7.6 Hz), 7.61 (1H, d, H7, J = 7.1 Hz), 7.63 (1H, d, H3′, J = 4.0 Hz), 7.70 (1H, d, H5, J = 8.0 Hz), 8.23 (1H, d, Hβ, J = 15.6 Hz), 8.41 (1H, s, H4). MS (m/z): 393 (M+, 2%), 82 (M+–C13H9NOClBr, 100%). Anal. Calcd for C17H11BrClNOS: C, 51.99; H, 2.82; N, 3.57. Found: C, 51.93; H, 2.75; N, 3.55.

(2E)-3-(2-Chloro-8-methylquinolin-3-yl)-1-(5-iodothien-2-yl)prop-2-en-1-one (2k)

Yield, 86%; yellow solid. mp 196–198°C. IR (KBr, cm−1): 1649 (C=O), 1596 (C=C), 1565 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.76 (3H, s, Me), 7.36 (1H, d, H4′, J = 3.8 Hz), 7.38 (1H, d, Hα, J = 15.6 Hz), 7.47 (1H, t, H6, J = 7.6 Hz), 7.51 (1H, d, H3′, J = 3.9 Hz), 7.61 (1H, d, H7, J = 7.0 Hz), 7.70 (1H, d, H5, J = 8.1 Hz), 8.23 (1H, d, Hβ, J = 15.6 Hz), 8.41 (1H, s, H4). MS (m/z): 439 (M+, 1%), 82 (M+–C13H9NOICl, 100%). Anal. Calcd for C17H11ClINOS: C, 46.44; H, 2.52; N, 3.19. Found: C, 46.39; H, 2.42; N, 3.13.

General procedure for the preparation of 2-chloro-3-[3-(aryl)-4,5-dihydro-1H-pyrazol-5-yl]-7/8-methylquinoline (3a–k) and (4a–k)

A mixture of chalcone (1a–k or 2a–k, 1.0 mmol) and hydrazine hydrate (3.0 mmol) in ethanol (10 ml) was refluxed. The crude product got precipitated within 8–15 min which was poured onto ice-cold water (50 ml). The precipitates were collected by filtration, washed with cold water followed by cold EtOH to obtain 2-pyrazolines which were recrystallised from EtOH (95%) to obtain pure compounds (3a–k and 4a–k).

2-Chloro-7-methyl-3-(3-thiophen-3-yl-4,5-dihydro-1H-pyrazol-5-yl)quinoline (3a)

Yield, 80%; colourless solid. mp 180–181°C. IR (KBr, cm−1): 3275 (NH), 1596 (C=N of pyrazoline ring), 1555 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.50 (3H, s, CH3), 2.95 (1H, dd, J = 16.3, 9.4 Hz, 4-Ha), 3.74 (1H, dd, J = 16.4, 10.6 Hz, 4-Hb), 5.38 (1H, t, J = 9.9 Hz, 5-H), 7.31 (1H, dd, H4′, J = 5.0 Hz, 2.8 Hz), 7.40 (1H, d, H5, J = 8.1 Hz), 7.62 (1H, dd, H5′, J = 4.9 Hz, 0.9 Hz), 7.73 (1H, d, H6, J = 8.3 Hz), 7.75 (1H, s, H8), 8.08 (1H, dd, H2′, J = 2.8 Hz, 1.0 Hz), 8.40 (1H, s, H4). MS (m/z): 327 (M+, 78.53%). Anal. Calcd for C17H14ClN3S: C, 62.28; H, 4.30; N, 12.82. Found: C, 62.24; H, 4.25; N, 12.80.

2-Chloro-7-methyl-3-[3-(3-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (3b)

Yield, 78%; yellow solid. mp 160–161°C. IR (KBr, cm−1): 3285 (NH), 1602 (C=N of pyrazoline ring), 1559 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.53–2.62 (s, 2× CH3), 2.84 (1H, dd, J = 16.3, 9.4 Hz, 4-Ha), 3.64 (1H, dd, J = 16.3, 10.4 Hz, 4-Hb), 5.29 (1H, t, J = 9.9 Hz, 5-H), 6.82 (1H, d, H4′, J = 5.0 Hz), 7.35 (1H, d, H5, J = 8.1 Hz), 7.35 (1H, d, H5′, J = 4.9 Hz), 7.74 (1H, d, H6, J = 8.5 Hz), 7.76 (1H, s, H8), 8.39 (1H, s, H4). MS (m/z): 341 (M+, 84.01%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.14; H, 4.65; N, 12.29.

2-Chloro-7-methyl-3-[3-(4-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (3c)

Yield, 83%; colourless solid. mp 200°C. IR (KBr, cm−1): 3280 (NH), 1599 (C=N of pyrazoline ring), 1555 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.30–2.50 (s, 2× CH3), 2.85 (1H, dd, J = 16.3, 9.3 Hz, 4-Ha), 3.66 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.30 (1H, t, J = 9.9 Hz, 5-H), 7.11 (1H, s, H5′), 7.37 (1H, d, H5, J = 8.1 Hz), 7.51 (1H, s, H3′), 7.74 (1H, d, H6, J = 8.3 Hz), 7.76 (1H, s, H8), 8.41 (1H, s, H4). MS (m/z): 341 (M+, 84.02%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.21; H, 4.69; N, 12.25.

2-Chloro-7-methyl-3-[3-(5-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (3d)

Yield, 87%; pale yellow solid. mp 198°C. IR (KBr, cm−1): 3275 (NH), 1595 (C=N of pyrazoline ring), 1558 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52–2.54 (s, 2× CH3), 2.85 (1H, dd, J = 16.3, 9.3 Hz, 4-Ha), 3.66 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.31 (1H, t, J = 9.9 Hz, 5-H), 6.66 (1H, d, H4′, J = 3.2 Hz), 6.85 (1H, d, H3′, J = 3.5 Hz), 7.37 (1H, d, H5, J = 8.1 Hz), 7.74 (1H, d, H6, J = 8.3 Hz), 7.76 (1H, s, H8), 8.40 (1H, s, H4). MS (m/z): 341 (M+, 84.04%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.23; H, 4.69; N, 12.31.

2-Chloro-3-[3-(2,5-dimethylthiophen-3-yl)-4,5-dihydro-1H-pyrazol-5-yl]-7-methylquinoline (3e)

Yield, 86%; off-white solid. mp 116–117°C. IR (KBr, cm−1): 3279 (NH), 1610 (C=N of pyrazoline ring), 1556 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.36–2.65 (s, 3× CH3), 2.82 (1H, dd, J = 16.2, 9.7 Hz, 4-Ha), 3.65 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.28 (1H, t, J = 10.0 Hz, 5-H), 6.86 (1H, s, H4′), 7.41 (1H, d, H5, J = 8.3 Hz), 7.72 (1H, d, H6, J = 8.3 Hz), 7.76 (1H, s, H8), 8.34 (1H, s, H4). MS (m/z): 355 (M+, 100%). Anal. Calcd. for C19H18ClN3S: C, 64.12; H, 5.10; N, 11.81. Found: C, 64.08; H, 5.05; N, 11.76.

2-Chloro-3-[3-(3-chlorothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-7-methylquinoline (3f)

Yield, 79%; colourless solid. mp 166167°C. IR (KBr, cm−1): 3288 (NH), 1608 (C=N of pyrazoline ring), 1560 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52 (3H, s, CH3), 3.15 (1H, dd, J = 16.9, 10.1 Hz, 4-Ha), 4.00 (1H, dd, J = 16.9, 10.8 Hz, 4-Hb), 5.39 (1H, t, J = 10.4 Hz, 5-H), 6.86 (1H, d, H4′, J = 5.2 Hz), 7.21 (1H, d, H5, J = 8.3 Hz), 7.32 (1H, d, H5′, J = 5.2 Hz), 7.76 (1H, d, H6, J = 8.6 Hz), 7.89 (1H, s, H8), 8.37 (1H, s, H4). MS (m/z): 361 (M+, 96.20%) 185 (M+–C10H7NCl, 100%). Anal. Calcd. for C17H13Cl2N3S: C, 56.36; H, 3.62; N, 11.60. Found: C, 56.32; H, 3.61; N, 11.58.

2-Chloro-3-[3-(5-chlorothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-7-methylquinoline (3g)

Yield, 83%; off-white solid. mp 205–207°C. IR (KBr, cm−1): 3284 (NH), 1605 (C=N of pyrazoline ring), 1560 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.50 (3H, s, CH3), 2.87 (1H, dd, J = 16.2, 10.0 Hz, 4-Ha), 3.71 (1H, dd, J = 16.2, 10.7 Hz, 4-Hb), 5.36 (1H, t, J = 10.3 Hz, 5-H), 6.82 (1H, d, H4′, J = 4.3 Hz), 7.28 (1H, d, H5, J = 8.3 Hz), 7.47 (1H, d, H3′, J = 4.3 Hz), 7.65 (1H, d, H6, J = 8.3 Hz), 7.69 (1H, s, H8), 8.34 (1H, s, H4). MS (m/z): 361 (M+, 100%). Anal. Calcd for C17H13Cl2N3S: C, 56.36; H, 3.62; N, 11.60. Found: C, 56.34 H, 3.59; N, 11.52.

2-Chloro-3-[3-(2,5-dichlorothiophen-3-yl)-4,5-dihydro-1H-pyrazol-5-yl]-7-methylquinoline (3 h)

Yield, 75%; off-white solid. mp 178–179°C. IR (KBr, cm−1): 3282 (NH), 1612 (C=N of pyrazoline ring), 1561 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52 (3H, s, CH3), 3.11 (1H, dd, J = 16.7, 9.9 Hz, 4-Ha), 3.98 (1H, dd, J = 16.7, 10.5 Hz, 4-Hb), 5.39 (1H, t, J = 10.2 Hz, 5-H), 6.97 (1H, s, H4′), 7.35 (1H, d, H5, J = 8.3 Hz), 7.72 (1H, d, H6, J = 8.2 Hz), 7.75 (1H, s, H8), 8.33 (1H, s, H4). MS (m/z): 397 (M+, 100%). Anal. Calcd. for C17H12Cl3N3S: C, 51.47; H, 3.05; N, 10.59. Found: C, 51.45; H, 3.02; N, 10.54.

3-[3-(3-Bromothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-2-chloro-7-methylquinoline (3i)

Yield, 92%; colourless solid. mp 170–171°C; IR (KBr, cm−1): 3279 (NH), 1608 (C=N of pyrazoline ring), 1556 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.53 (3H, s, CH3), 3.19 (1H, dd, J = 16.8, 10.1 Hz, 4-Ha), 4.06 (1H, dd, J = 16.8, 10.8 Hz, 4-Hb), 5.39 (1H, t, J = 10.4 Hz, 5-H), 6.95 (1H, d, H4′, J = 5.5 Hz), 7.35 (1H, d, H5, J = 8.2 Hz), 7.21 (1H, d, H5′, J = 5.5 Hz), 7.72 (1H, d, H6, J = 8.6 Hz), 7.74 (1H, s, H8), 8.38 (1H, s, H4). MS (m/z): 407 (M+, 100%). Anal. Calcd. for C17H13BrClN3S: C, 50.20; H, 3.22; N, 10.33. Found: C, 50.12; H, 3.14; N, 10.30.

3-[3-(5-Bromothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-2-chloro-7-methylquinoline (3j)

Yield, 76%; colourless solid. mp 195°C. IR (KBr, cm−1): 3282 (NH), 1600 (C=N of pyrazoline ring), 1552 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52 (3H, s, CH3), 2.88 (1H, dd, J = 16.2, 9.9 Hz, 4-Ha), 3.71 (1H, dd, J = 16.2, 10.7 Hz, 4-Hb), 5.36 (1H, t, J = 10.3 Hz, 5-H), 6.86 (1H, d, H4′, J = 4.2 Hz), 7.36 (1H, d, H5, J = 8.3 Hz), 7.43 (1H, d, H3′, J = 4.2 Hz), 7.74 (1H, d, H6, J = 8.3 Hz), 7.75 (1H, s, H8), 8.35 (1H, s, H4). MS (m/z): 407 (M+, 100%). Anal. Calcd. for C17H13BrClN3S: C, 50.20; H, 3.22; N, 10.33. Found: C, 50.15; H, 3.19; N, 10.25.

2-Chloro-3-[3-(5-iodothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-7-methylquinoline (3k)

Yield, 85%; colourless solid. mp 212°C. IR (KBr, cm−1): 3281 (NH), 1610 (C=N of pyrazoline ring), 1550 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.52 (3H, s, CH3), 2.87 (1H, dd, J = 16.2, 9.9 Hz, 4-Ha), 3.71 (1H, dd, J = 16.2, 10.7 Hz, 4-Hb), 5.36 (1H, t, J = 10.3 Hz, 5-H), 6.71 (1H, d, H4′, J = 4.2 Hz), 7.15 (1H, d, H3′, J = 4.2 Hz), 7.34 (1H, d, H5, J = 8.4 Hz), 7.74 (1H, d, H6, J = 8.3 Hz), 7.75 (1H, s, H8), 8.35 (1H, s, H4). MS (m/z): 453 (M+, 100%). Anal. Calcd. for C17H13ClIN3S: C, 45.00; H, 2.89; N, 9.26. Found: C, 44.95; H, 2.85; N, 9.23.

2-Chloro-8-methyl-3-(3-thiophen-3-yl-4,5-dihydro-1H-pyrazol-5-yl)quinoline (4a)

Yield, 72%; colourless solid. mp 195–196°C. IR (KBr, cm−1): 3274 (NH), 1595 (C=N of pyrazoline ring), 1550 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.70 (3H, s, CH3), 2.97 (1H, dd, J = 16.4, 9.4 Hz, 4-Ha), 3.75 (1H, dd, J = 16.4, 10.7 Hz, 4-Hb), 5.39 (1H, t, J = 9.9 Hz, 5-H), 7.32 (1H, dd, H4′, J = 5.0 Hz, 2.8 Hz), 7.45 (1H, t, H6, J = 7.6 Hz), 7.55 (1H, d, H7, J = 7.0 Hz), 7.60 (1H, d, H5′, J = 4.6 Hz, 1.0 Hz), 7.67 (1H, d, H5, J = 6.6 Hz), 8.08 (1H, dd, H2′, J = 2.7 Hz, 1.0 Hz), 8.39 (1H, s, H4). MS (m/z): 327 (M+, 70.30%). Anal. Calcd. for C17H14ClN3S: C, 62.28; H, 4.30; N, 12.82. Found: C, 62.22; H, 4.22; N, 12.78.

2-Chloro-8-methyl-3-[3-(3-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (4b)

Yield, 67%; colourless solid. mp 130–131°C. IR (KBr, cm−1): 3277 (NH), 1605 (C=N of pyrazoline ring), 1552 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.63–2.73 (s, 2× CH3), 2.85 (1H, dd, J = 16.3, 9.4 Hz, 4-Ha), 3.66 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.31 (1H, t, J = 9.9 Hz, 5-H),6.82 (1H, d, H4′, J = 5.1 Hz), 7.45 (1H, t, H6, J = 7.6 Hz), 7.33 (1H, d, H5′, J = 5.1 Hz), 7.54 (1H, d, H7, J = 7.0 Hz), 7.69 (1H, d, H5, J = 7.9 Hz), 8.38 (1H, s, H4). MS (m/z): 341 (M+, 59.47%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.22; H, 4.75; N, 12.23.

2-Chloro-8-methyl-3-[3-(4-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (4c)

Yield, 71%; colourless solid. mp 182°C. IR (KBr, cm−1): 3281 (NH), 1595 (C=N of pyrazoline ring), 1555 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.30–2.72 (s, 2× CH3), 2.87 (1H, dd, J = 16.3, 9.3 Hz, 4-Ha), 3.69 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.31 (1H, t, J = 9.9 Hz, 5-H) 7.11 (1H, s, H5′), 7.44 (1H, t, H6, J = 7.5 Hz), 7.55 (1H, d, H7, J = 7.0 Hz), 7.69 (1H, d, H5, J = 7.0 Hz), 7.52 (1H, s, H3′), 8.37 (1H, s, H4). MS (m/z): 341 (M+, 60.02%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.20; H, 4.69; N, 12.25.

2-Chloro-8-methyl-3-[3-(5-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinoline (4d)

Yield, 80%; pale yellow solid. mp 209–210°C. IR (KBr, cm−1): 3278 (NH), 1592 (C=N of pyrazoline ring), 1550 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.53–2.72 (s, 2× CH3), 2.86 (1H, dd, J = 16.3, 9.3 Hz, 4-Ha), 3.67 (1H, dd, J = 16.3, 10.5 Hz, 4-Hb), 5.31 (1H, t, J = 9.9 Hz, 5-H), 6.66 (1H, d, H4′, J = 3.0 Hz), 6.86 (1H, d, H3′ J = 3.4 Hz), 7.44 (1H, t, H6, J = 7.6 Hz), 7.54 (1H, d, H7, J = 7.0 Hz), 7.62 (1H, d, H5, J = 8.1 Hz), 8.33 (1H, s, H4). MS (m/z): 341 (M+, 59.81%). Anal. Calcd. for C18H16ClN3S: C, 63.24; H, 4.72; N, 12.29. Found: C, 63.23; H, 4.70; N, 12.27.

2-Chloro-3-[3-(2,5-dimethylthiophen-3-yl)-4,5-dihydro-1H-pyrazol-5-yl]-8-methylquinoline (4e)

Yield, 88%; brown solid. mp 126–127°C. IR (KBr, cm−1): 3282 (NH), 1609 (C=N of pyrazoline ring), 1553 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.42–2.73 (s, 3× Me), 2.84 (1H, dd, J = 16.3, 9.7 Hz, 4-Ha), 3.68 (1H, dd, J = 16.3, 10.6 Hz, 4-Hb), 5.30 (1H, t, J = 10.0 Hz, 5-H), 6.86 (1H, s, H4′), 7.42 (1H, t, H6, J = 7.7 Hz), 7.54 (1H, d, H7, J = 7.0 Hz), 7.68 (1H, d, H5, J = 8.1 Hz), 8.34 (1H, s, H4). MS (m/z): 355 (M+, 100%). Anal. Calcd. for C19H18ClN3S: C, 64.12; H, 5.10; N, 11.81. Found: C, 64.10; H, 5.08; N, 11.79.

2-Chloro-3-[3-(3-chlorothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-8-methylquinoline (4f)

Yield, 81%; yellowish brown solid. mp 152°C. IR (KBr, cm−1): 3277 (NH), 1610 (C=N of pyrazoline ring), 1559 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 3.16 (1H, dd, J = 16.9, 10.2 Hz, 4-Ha), 4.01 (1H, dd, J = 16.9, 10.8 Hz, 4-Hb), 5.39 (1H, t, J = 10.4 Hz, 5-H), 6.87 (1H, d, H4′, J = 5.4 Hz), 7.41 (1H, t, H6, J = 7.6 Hz), 7.54 (1H, d, H7, J = 7.0 Hz), 7.32 (1H, d, H5′, J = 5.4 Hz), 7.65 (1H, d, H5, J = 8.1 Hz), 8.37 (1H, s, H4). MS (m/z): 361 (M+, 100%). Anal. Calcd. for C17H13Cl2N3S: C, 56.36; H, 3.62; N, 11.60. Found: C, 56.34; H, 3.58; N, 11.54.

2-Chloro-3-[3-(5-chlorothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-8-methylquinoline (4g)

Yield, 80%; pale yellow solid. mp 230–232°C. IR (KBr, cm−1): 3285 (NH), 1603 (C=N of pyrazoline ring), 1560 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 2.89 (1H, dd, J = 16.3, 10.1 Hz, 4-Ha), 3.71 (1H, dd, J = 16.3, 10.7 Hz, 4-Hb), 5.39 (1H, t, J = 10.3 Hz, 5-H), 6.85 (1H, d, H4′, J = 4.2 Hz), 7.42 (1H, t, H6, J = 7.6 Hz), 7.56 (1H, d, H7, J = 7.0 Hz), 7.48 (1H, d, H3′, J = 4.4 Hz), 7.63 (1H, d, H5, J = 8.0 Hz), 8.35 (1H, s, H4). MS (m/z): 361 (M+, 100%). Anal. Calcd. for C17H13Cl2N3S: C, 56.36; H, 3.62; N, 11.60. Found: C, 56.31; H, 3.56; N, 11.55.

2-Chloro-3-[3-(2,5-dichlorothiophen-3-yl)-4,5-dihydro-1H-pyrazol-5-yl]-8-methylquinoline (4h)

Yield, 75%; yellowish brown solid. mp 153°C. IR (KBr, cm−1): 3280 (NH), 1615 (C=N of pyrazoline ring), 1560 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 3.15 (1H, dd, J = 16.8, 10.0 Hz, 4-Ha), 4.00 (1H, dd, J = 16.8, 10.5 Hz, 4-Hb), 5.40 (1H, t, J = 10.3 Hz, 5-H), 6.96 (1H, s, H4′), 7.41 (1H, t, H6, J = 7.6 Hz), 7.56 (1H, d, H7, J = 6.8 Hz), 7.62 (1H, d, H5, J = 8.1 Hz), 8.35 (1H, s, H4). MS (m/z): 397 (M+, 100%). Anal. Calcd. for C17H12Cl3N3S: C, 51.47; H, 3.05; N, 10.59. Found: C, 51.41; H, 3.00; N, 10.56.

3-[3-(3-Bromothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-2-chloro-8-methylquinoline (4i)

Yield, 77%; pale yellow solid. mp 166–168°C. IR (KBr, cm−1): 3279 (NH), 1607 (C=N of pyrazoline ring), 1555 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 3.21 (1H, dd, J = 16.9, 10.2 Hz, 4-Ha), 4.10 (1H, dd, J = 16.8, 10.8 Hz, 4-Hb), 5.40 (1H, t, J = 10.4 Hz, 5-H), 6.86 (1H, d, H4′, J = 5.5 Hz), 7.43 (1H, t, H6, J = 7.6 Hz), 7.21 (1H, d, H5′, J = 5.5 Hz), 7.54 (1H, d, H7, J = 7.1 Hz), 7.65 (1H, d, H5, J = 8.0 Hz), 8.39 (1H, s, H4). MS (m/z): 407 (M+, 100%). Anal. Calcd. for C17H13BrClN3S: C, 50.20; H, 3.22; N, 10.33. Found: C, 50.14; H, 3.18; N, 10.29.

3-[3-(5-Bromothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-2-chloro-8-methylquinoline (4j)

Yield, 80%; pale yellow solid. mp 215–216°C. IR (KBr, cm−1): 3282 (NH), 1597 (C=N of pyrazoline ring), 1552 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 2.89 (1H, dd, J = 16.2, 9.9 Hz, 4-Ha), 3.71 (1H, dd, J = 16.2, 10.6 Hz, 4-Hb), 5.36 (1H, t, J = 10.3 Hz, 5-H), 6.87 (1H, d, H4′, J = 4.2 Hz), 7.42 (1H, t, H6, J = 7.6 Hz), 7.55 (1H, d, H7, J = 7.1 Hz), 7.43 (1H, d, H3′, J = 4.2 Hz), 7.63 (1H, d, H5, J = 8.0 Hz), 8.36 (1H, s, H4). MS (m/z): 407 (M+, 100%). Anal. Calcd. for C17H13BrClN3S: C, 50.20; H, 3.22; N, 10.33. Found: C, 50.19 H, 3.17; N, 10.28.

2-Chloro-3-[3-(5-iodothiophen-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]-8-methylquinoline (4k)

Yield, 82%; pale yellow solid. mp 178°C. IR (KBr, cm−1): 3280 (NH), 1605 (C=N of pyrazoline ring), 1550 (C=N of quinoline ring). 1H-NMR (CDCl3) δ: 2.72 (3H, s, CH3), 2.90 (1H, dd, J = 16.3, 9.9 Hz, 4-Ha), 3.73 (1H, dd, J = 16.3, 10.6 Hz, 4-Hb), 5.37 (1H, t, J = 10.2 Hz, 5-H), 6.71 (1H, d, H4′, J = 4.0 Hz), 7.42 (1H, t, H6, J = 7.6 Hz), 7.16 (1H, d, H3′, J = 4.1 Hz), 7.56 (1H, d, H7, J = 7.0 Hz), 7.63 (1H, d, H5, J = 8.1 Hz), 8.36 (1H, s, H4). MS (m/z): 453 (M+, 100%). Anal. Calcd. for C17H13ClIN3S: C, 45.00; H, 2.89; N, 9.26. Found: C, 44.98; H, 2.81; N, 9.25.

In vitro antileishmanial assay

The title compounds (1a–k and 2a–k) and (3a–k and 4a–k) were tested for the antileishmanial activity using L. major promastigotes as parasites for in vitro screening. Parasites were cultured at 24°C in shaking incubator on M 199 medium containing foetal bovine serum (10%); HEPES (25 mM), and penicillin and streptomycin (0.22 μg each) (Ali et al., 1997).

Each compound (1 mg) was dissolved in DMSO (1 ml) and Amphotericin B (1 mg) taken in DMSO (1 ml) was used as a positive control. Parasites were taken from lag phase of their growth and were centrifuged at 3000 rpm for 3 min. The parasite density was maintained at 2 × 106 cells/ml by diluting with fresh culture medium. In 96-well plates, 180 μl of medium was added in different wells. The experimental compound (20 μl) was added in medium and serially diluted. Parasite culture (100 μl) was added in all wells. In negative controls, DMSO was serially diluted in medium; while the positive control, contained varying concentrations of standard antileishmanial compound, i.e. Amphotercin B. The plates were incubated for 72 h at 24°C. The culture was examined microscopically on an improved neubaur counting chamber and IC50 values of compounds possessing antileishmanial activity were calculated. All assays were run in duplicate. The results are summarized in Table 2. IC50 values of compounds were determined using prism windows-based software.

After running the samples, % of inhibition is calculated in serial dilution methods. It depends on the activity of the compounds; some of them show in 4-6-7 or 10 dilution the inhibitory concentration. Subsequently, we count the number of parasite in neubauer chamber (0.0025 mm2) and implement the result manually in the prism windows-based software.