Synthesis and Analgesic Activity of 4,7-Dimethyl-3,4,4a,5,8,8a-Hexahydro-2H-Chromen-4,8-Diols Containing Thiophene Substituents

Hexahydro-2H-chromenes with thiophene fragments were synthesized via reactions of a p-menthane monoterpenoid diol with several thiophenecarboxaldehydes. Most of the synthesized compounds with an additional thiophene fragment displayed analgesic activity in vivo tests at a dose of 10 mg/kg. It was found that the activity in either an acetate-writhing test or a hot-plate test depended on the type and location of substituent in the heteroaromatic ring.

The discovery of new analgesic drugs is one of the most important tasks of contemporary pharmacology because those used currently are ineffective, especially for relieving chronic pain, and have many side effects [1–3]. The problem is exacerbated by the sharp drop in the last two decades in the number of new analgesics with regulatory approval [4].

Recently, we found that compounds 1 with the 3,4,4a,5,8,8a-hexahydro-2H-chromene skeleton that were synthesized by reacting the monoterpenoid (1R,2R,6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-en-1,2-diol (2) with aromatic aldehydes 3 in the presence of K10 montmorillonite clay (Scheme 1) exhibited high analgesic activity [5]. Starting 2 could be synthesized in three steps from the very common monoterpenoid (–)-verbenone (4) using available reagents [6].

Scheme 1

ᅟ

Heteroaromatic fragments instead of an aromatic ring with methoxy and/or hydroxy substituents can also produce analogs of 1 with high analgesic activity. The goals of the present work were to synthesize type 1 compounds containing a thiophene substituent and to study their analgesic activity.

The study began by reacting diol 2 with thiophene-2-carbaldehyde (5a) using K10 montmorillonite clay as a catalyst, which was used successfully earlier to perform similar transformations [7–10]. The reaction was carried out without a solvent. The reagents were evenly applied to the clay using CH₂C_l2, which was then evaporated. The reaction mixture was stored for the required time at room temperature.

The reaction of 2 and 5a occurred in 45 min, giving target product 6a in 42% yield (Scheme 1), in contrast with previously studied reactions of 2 with aromatic aldehydes in the presence of K10 clay, complete conversion of which required up to 24 h [11]. The reaction time increased sharply (>20 h) and a complicated mixture of unidentified compounds formed if the reaction was performed without removing the solvent. Like for 1, 6a was formed as a mixture of diastereomers at the C atom bonded to the methyl and hydroxyl. The (S)–(R) isomeric ratio in this instance was 3.3:1.

Introducing a Br atom or methyl substituent into the aldehyde increased the reaction time to 2–2.5 h and gave product yields of 47–55% (Scheme 1). Dehydration product 7 was isolated in 26% yield together with target 6f (38% yield) from the reaction mixture if 5-nitrothiophene-2-carbaldehyde (5f) was used (Scheme 1).

The reaction of diol 2 with 4,5-dibromothiophene-2-carbaldehyde (5g) required a whole day for complete conversion of starting aldehyde 5g with a 50% excess of 2. Besides chromenes 6g and 8, compound 9 with the 1,3-benzodioxine skeleton was obtained in 19% yield (Scheme 2). Compounds with this skeleton were observed from the reaction of aldehydes with cis-verbenol epoxide [12] but not with 2. The exception was the reaction of 2 with 3-hydroxy-4-methoxybenzaldehyde, which also produced a compound with the 1,3-benzodioxine skeleton but in very low (3%) yield [13].

Scheme 2

ᅟ

The reaction of diol 2 with 3-thiophenecarboxaldehyde (10) in the presence of K10 clay formed heterocyclic product 11 in 54% yield (Scheme 2).

In all instances, diastereomers at the 4-position [(S)–(R) isomeric ratio given in parentheses after the yield in Scheme 2] were formed in comparable amounts.

The isomerism of (S)- and (R)-6a–g and 11 was due to different configurations of the methyl and hydroxyl groups on the same C atom. The ratio of (S)- and (R)-diastereomers was determined from PMR spectra from the ratio of H-3 peak areas. The vicinal spin–spin coupling constants (SSCC) between H-3 and H-4 and also between H-6 and H-7 were consistent with axial H-3 and H-6 in 6a–g and 11. Conversely, the vicinal SSCC between H-1 and H-10 indicated that they were equatorial. The CH₃-15 resonances in (S)-6f, (S)-6g, and (S)-11 appeared as doublets with W-SSCC ⁴J₁₅,4a ~ 0.6–0.7 Hz, which indicated that the methyl was axial. The same constant was also observed for (S)-6b–(S)-6e with artificial line narrowing. This confirmed that the methyls were axial. As expected, all (R)-compounds 6a–g and 11 had axial OH groups that caused paramagnetic shifts of the H-1 (δ ~ 0.4 ppm) and H-3 (δ ~ 0.3 ppm) resonances through 1,3-diaxial coupling. Resonances in 13C NMR spectra were assigned using 2D ¹³C–¹H spectra for direct SSCC (¹JC,H = 160 Hz).

Analgesic activity of the synthesized heterocyclic compounds was studied at a dose of 10 mg/kg using standard experimental acetic-writhing [14] and hot-plate [15] mouse pain models. The reference drug was sodium diclofenac injected at the same dose.

Table 1 presents data for 6a and 11 with unsubstituted heteroaromatic rings that did not exhibit any analgesic activity. Introducing a Br atom into the molecule (6b and 6c) produced significant analgesic activity in the hot-plate test although 6b and 6c were inactive in the acetic-writhing test. This was somewhat unexpected because analogous compounds containing a substituted phenyl fragment instead of a heteroaromatic one usually demonstrated analgesic activity in the acetic-writhing test and much more rarely in the hot-plate test [5].

Table 1 Analgesic Activity of 6a–g, 8, 9, 11, and Sodium Diclofenac at a Dose of 10 mg/kg

Replacing the heteroaromatic 5-Br by a methyl on going from 6c to 6e reversed the nature of the observed effect, i.e., 6e decreased significantly the residence time of the animals on the hot plate, thereby causing hyperalgesia instead of the analgesic effect found for 6c. Moving the methyl from the 5- to the 3-position (6d) produced an analgesic effect in the aceticwrithing test. Hyperalgesia in the hot-plate test appeared only as a trend. Statistically significant differences were not found.

Debrominated 6g, 8, and 9 did not exhibit significant analgesic activity in both tests.

Compound 6f with a nitro group was the most effective drug in the acetic-writhing test and was about as effective as the reference drug sodium diclofenac. However, it was inactive in the hot-plate test.

Thus, compounds with the hexahydro-2H-chromene skeleton were synthesized via the reaction of monoterpenoid 2 with heteroaromatic aldehydes contain S atoms. Compounds 6a and 11 with unsubstituted heteroaromatic substituents did not show any analgesic activity. Compounds 6b and 6c with one Br atom on the heteroaromatic ring were active at a dose of 10 mg/kg in the hot-late test but were inactive in the acetic-writhing test. Also, 6f with a nitro group demonstrated an analgesic effect in the acetic-writhing test although it was inactive in the hot-plate test. Replacing the 5-Br on the thiophene ring in 6c by a methyl on going to 6e produced hyperalgesia instead of an analgesic effect.

Experimental

We used commercially available reagents (Sigma-Aldrich, Acros) of at least 98% purity. (1R,2R,6S)-3-Methyl-6-(prop-1-en-2-yl)cyclohex-3-en-1,2-diol (2) {[α] ³¹_D –49.1° (c 2.6, CHCl₃)} was synthesized from (–)-verbenone (4) (Sigma-Aldrich) by the published method [6]. The catalyst was K10 clay (Fluka) that was calcined at 105°C for 3 h immediately before use. CH₂Cl₂ was passed over calcined Al₂O₃.

The reaction mixture was separated by column chromatography (CC) over silica gel (Macherey-Nagel, 60–200 μ) with elution by EtOAc (0–100%) in hexane. Fractions were analyzed by GC on an Agilent 7820A instrument with an HP-5 quartz column (copolymer of 5% diphenyl- and 95% dimethoxysiloxane, 30 m × 0.25 mm, 0.25 ×m), flame-ionization detector, and He carrier gas (flow rate 2 mL/min, flow division 99:1). GC-MS spectra were recorded on a Hewlett–Packard 5890/II GC with an HP MSD 5971 quadrupole mass spectrometer as the detector, an HP-5ms quartz column (30000 × 0.25 mm), and He carrier gas.

PMR and ¹³C NMR spectra were recorded using resonances of CD(H)Cl₃ (δ_H 7.24, δ_C 76.90 ppm) or CD₃OD(H) (δ_H 3.34, δ_C 49.00 ppm) as internal standards on a Bruker DRX-500 spectrometer (¹H 500.13 MHz, ¹³C 125.76 MHz). Structures of products were established by analyzing PMR and ¹³C NMR spectra using ¹H–¹H double resonance, 2D homonuclear 1H–1H correlations (1H–1H COSY), and 2D heteronuclear ¹³C–¹H correlations for direct spin–spin coupling constants (C–H COSY, ¹J_C,H = 160 Hz). Multiplicities of resonances in ¹³C NMR spectra were determined from spectra recorded in J-modulation mode (JMOD); the elemental composition, from mass spectra recorded on a Thermo Scientific DFS spectrometer in full-scan mode over the range 0–500 m/z with electron-impact ionization at 70 eV and direct sample introduction. Specific rotation was measured on a PolAAr 3005 polarimeter from CHCl₃ solutions.

Reaction of (1 R ,2 R ,6 S )-3-Methyl-6-(prop-1-en-2-yl)cyclohex-3-en-1,2-diol (2) with Aldehydes 5a–g and 11. General Method. A suspension of K10 clay in CH₂Cl₂ (5 mL) was treated with a solution of the appropriate aldehyde in CH₂Cl₂ (3 mL) and then a solution of 2 in CH₂Cl₂ (3 mL). The solvent was distilled off. The reaction mixture was stored at room temperature for the required time and worked up with EtOAc (10 mL). The catalyst was filtered off. The solvent was distilled off. The solid was separated by CC over silica gel.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-4,7-Dimethyl-2-(thiophen-2-yl)-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6a). The reaction of 2 (0.300 g, 1.79 mmol) with 5a (0.200 g, 1.79 mmol) in the presence of K10 clay (1.00 g) for 45 min produced an isomeric mixture of (S)- and (R)-6a [(S)–(R) ratio 3.1:1] (0.197 g, 40%) and (S)-6a (0.012 g, 2%). The overall yield of 6a was 42% [(S)–(R) ratio 3.3:1].

( S )-6a. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.52 (3H, s, CH₃-15), 1.80 (3H, br.s, CH₃-16), 1.79–1.84 (1H, m, H_a-6), 1.84 (1H, dd, ²J = 13.3, J_4e,3a = 2.6, H_e-4), 2.09 (1H, dd, ²J = 13.3, J_4a,3a = 11.8, H_a-4), 2.14–2.20 (2H, m, H-7), 3.84 (1H, br.t, J_1e,6a(10e) = 2.2, H_e-1), 3.93 (1H, br.s, H_e-10), 4.68 (1H, dd, J_3a,4a = 11.8, J_3a,4e = 2.6, H_a-3), 5.61–5.65 (1H, m, H-8), 6.93 (1H, dd, J_13,12 = 5.0, J_13,14 = 3.5, H-13), 6.97 (1H, br.d, J_14,13 = 3.5, H-14), 7.22 (1H, dd, J_12,13 = 5.0, J_12,14 = 1.0, H-12). ¹³C NMR spectrum (CDCl₃, δ, ppm): 77.89 (d, C-1), 73.30 (d, C-3), 42.73 (t, C-4), 70.92 (s, C-5), 38.49 (d, C-6), 22.55 (t, C-7), 124.69 (d, C-8), 131.26 (s, C-9), 70.52 (d, C-10), 144.75 (s, C-11), 124.79 (d, C-12), 126.35 (d, C-13), 123.87 (d, C-14), 27.10 (q, C-15), 20.63 (q, C-16). [α] ²⁷_D –62° (c 3, MeOH). Found m/z 280.1132 [M]⁺, C₁₅H₂₀O₃S. Calcd [M]⁺ 280.1128.

( R )-6a. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.26 (3H, s, CH₃-15), 1.68 (1H, br.t, J_6,7 = 8.5, H_a-6), 1.77 (1H, ddd, ²J = 13.9, J_4e,3a = 2.8, J_4e,6a = 1.2, H_e-4), 1.80 (3H, m, all J ≤ 2.5, CH₃-16), 1.93 (1H, dd, ²J = 13.9, J_4a,3a = 11.7, H_a-4), 1.97–2.03 (2H, m, H-7), 3.93 (1H, br.s, H_e-10), 4.26 (1H, dd, J_1e,10e = 2.2, J_1e,6a = 2.1, H_e-1), 5.04 (1H, dd, J_3a,4a = 11.7, J_3a,4e = 2.8, H_a-3), 5.54–5.58 (1H, m, H-8), 6.92 (1H, dd, J_13,12 = 5.0, J_13,14 = 3.5, H-13), 6.95 (1H, ddd, J_14,13 = 3.5, J_14,12 = 1.2, J_14,3a = 0.8, H-14), 7.19 (1H, dd, J_12,13 = 5.0, J_12,14 = 1.2, H-12). ¹³C NMR spectrum (CDCl₃, δ, ppm): 75.47 (d, C-1), 71.73 (d, C-3), 41.82 (t, C-4), 70.73 (s, C-5), 38.20 (d, C-6), 24.45 (t, C-7), 124.03 (d, C-8), 131.74 (s, C-9), 70.41 (d, C-10), 145.51 (s, C-11), 124.47 (d, C-12), 126.32 (d, C-13), 123.67 (d, C-14), 28.35 (q, C-15), 20.73 (q, C-16). Found m/z 280.1132 [M]⁺, C₁₅H₂₀O₃S. Calcd [M]⁺ 280.1128.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-2-(4-Bromothiophen-2-yl)-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6b). The reaction of 2 (0.300 g, 1.79 mmol) with 5b (0.340 g, 1.79 mmol) in the presence of K10 clay (1.30 g) for 150 min produced 6b [(S)–(R) ratio 1:1] (0.324 g, 51%).

( S )-6b. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.48 (3H, s, CH₃-15), 1.76 (1H, ddd, ²J = 13.0, J_4e,3a = 2.8, J_4e,6a = 1.1, H_e-4), 1.79 (3H, br.s, CH₃-16), 1.78–1.83 (1H, m, H_a-6), 1.99 (1H, dd, ²J = 13.0, J_4a,3a = 12.0, H_a-4), 2.05–2.20 (2H, m, H-7), 3.79 (1H, dd, J_1e,10e = 2.3, J_1e,6a = 2.0, H_e-1), 3.88 (1H, br.s, H_e-10), 4.60 (1H, ddd, J_3a,4a = 12.0, J_3a,4e = 2.8, J_3a,14 = 0.7, H_a-3), 5.59–5.62 (1H, m, H-8), 6.86 (1H, dd, J_14,12 = 1.5, J_14,3a = 0.7, H-14), 7.09 (1H, d, J_12,14 = 1.5, H-12). ¹³C NMR spectrum (CDCl₃, δ, ppm): 77.89 (d, C-1), 72.81 (d, C-3), 42.29 (t, C-4), 70.77 (s, C-5), 38.30 (d, C-6), 22.49 (t, C-7), 124.55 (d, C-8), 131.17 (s, C-9), 70.33 (d, C-10), 146.05 (s, C-11), 121.86 (d, C-12), 108.92 (s, C-13), 126.37 (d, C-14), 26.96 (q, C-15), 20.61 (q, C-16). Found m/z 358.0233 [M]⁺, C₁₅H₁₉O₃SBr. Calcd [M]⁺ 358.0233.

R )-6b. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.24 (3H, s, CH₃-15), 1.68 (1H, ddm, J_6a,7a = 10.8, J_6a,7e = 6.6, H_a-6), 1.73 (1H, ddd, 2_{J = 14}.1, J_4e,3a = 2.9, J_4e,6a = 1.3, H_e-4), 1.79 (3H, br.s, CH₃-16), 1.83 (1H, dd, ²J = 14.1, J_4a,3a = 11.5, H_a-4), 1.88–2.01 (2H, m, H-7), 3.90 (1H, br.s, H_e-10), 4.23 (1H, dd, J_1e,10e = 2.3, J_1e,6a = 2.0, H_e-1), 4.95 (1H, ddd, J_3a,4a = 11.5, J_3a,4e = 2.9, J_3a,14 = 0.7, H_a-3), 5.53–5.56 (1H, m, H-8), 6.84 (1H, dd, J_14,12 = 1.5, J_14,3a = 0.7, H-14), 7.08 (1H, d, J_12,14 = 1.5, H-12). ¹³C NMR spectrum (CDCl₃, δ, ppm): 75.44 (d, C-1), 71.31 (d, C-3), 41.34 (t, C-4), 70.64 (s, C-5), 37.99 (d, C-6), 24.34 (t, C-7), 123.93 (d, C-8), 131.64 (s, C-9), 70.31 (d, C-10), 146.82 (s, C-11), 121.60 (d, C-12), 108.88 (s, C-13), 126.11 (d, C-14), 28.22 (q, C-15), 20.71 (q, C-16). Found m/z 358.0233 [M]⁺, C₁₅H₁₉O₃SBr. Calcd [M]⁺ 358.0233.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-2-(5-Bromothiophen-2-yl)-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6c). The reaction of 2 (0.300 g, 1.79 mmol) with 5c (0.340 g, 1.79 mmol) in the presence of K10 clay (1.30 g) for 150 min produced an isomeric mixture of (S)- and (R)-6c [(S)–(R) ratio 1.8:1] (0.300 g, 41%) and (R)-6c (0.038 g, 6%). The overall yield of 6c was 47% [(S)–(R) ratio 1.3:1].

( S )-6c. ¹H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.47 (3H, s, CH₃-15), 1.76 (1H, ddd, J = 13.1, 2.8, 1.2, H_e-4), 1.79 (3H, m, all J ≤ 2.5, CH₃-16), 1.80–1.85 (1H, m, H_a-6), 2.01 (1H, dd, J = 13.1, 12.0, H_a-4), 2.05–2.20 (2H, m, H-7), 3.79 (1H, dd, J = 2.4, 2.1, H_e-1), 3.82 (1H, br.s, H_e-10), 4.62 (1H, ddd, J = 12.0, 2.8, 0.8, H_a-3), 5.60–5.63 (1H, m, H-8), 6.73 (1H, dd, J = 3.8, 0.8, H-14), 6.88 (1H, d, J = 3.8, H-13). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 78.75 (d, C-1), 73.76 (d, C-3), 42.19 (t, C-4), 70.62 (s, C-5), 38.72 (d, C-6), 23.00 (t, C-7), 124.75 (d, C-8), 131.52 (s, C-9), 70.36 (d, C-10), 147.33 (s, C-11), 111.95 (s, C-12), 129.54 (d, C-13), 124.47 (d, C-14), 26.79 (q, C-15), 20.83 (q, C-16). Found m/z 358.0232 [M]⁺, C₁₅H₁₉O₃SBr. Calcd [M]⁺ 358.0233.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-4,7-Dimethyl-2-(3-methylthiophen-2-yl)-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6d). The reaction of 2 (0.300 g, 1.79 mmol) with 5d (0.230 g, 1.83 mmol) in the presence of K10 clay (1.00 g) for 120 min produced a reaction mixture that was treated with CHCl₃. The resulting precipitate was filtered off to afford (S)-6d (0.074 g, 14%). The residue was separated by CC over silica gel to afford an isomeric mixture of (S)- and (R)-6d [(S)–(R) ratio 1.4:1] (0.215 g, 41%). The overall yield of 6d was 55% [(S)–(R) ratio 2.2:1].

( S )-6d. ¹H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.52 (3H, s, CH₃-15), 1.71 (1H, ddd, J = 13.3, 2.7, 1.1, H_e-4), 1.79 (3H, m, all J ≈ 2.5, CH₃-16), 1.87 (1H, br.t, J ≈ 8.5, H_a-6), 2.11 (1H, dd, J = 13.3, 12.1, H_a-4), 2.15–2.20 (2H, m, H-7), 2.24 (3H, s, CH₃-17), 3.82 (1H, br.s, H_e-10), 3.83 (1H, br.t, J ≈ 2.2, H_e-1), 4.76 (1H, dd, J = 12.1, 2.7, H_a-3), 5.61–5.65 (1H, m, H-8), 6.79 (1H, d, J = 5.1, H-13), 7.14 (1H, d, J = 5.1, H-12). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 79.15 (d, C-1), 72.54 (d, C-3), 42.60 (t, C-4), 70.96 (s, C-5), 39.04 (d, C-6), 23.38 (t, C-7), 124.96 (d, C-8), 131.83 (s, C-9), 70.63 (d, C-10), 138.45 (s, C-11), 123.74 (d, C-12), 130.52 (d, C-13), 134.98 (s, C-14), 26.93 (q, C-15), 20.92 (q, C-16), 13.87 (q, C-17). [α] ²⁵_D –112° (c 7, MeOH). Found m/z 294.1279 [M]⁺, C₁₆H₂₂O3S. Calcd [M]⁺ 294.1284.

( R )-6d. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.25 (3H, s, CH₃-15), 1.64–1.71 (2H, m, H_e-4, H_a-6), 1.79 (3H, m, all J ≤ 2.5, CH₃-16), 1.92 (1H, dd, J = 14.1, 11.8, H_a-4), 1.99–2.05 (2H, m, H-7), 2.22 (3H, s, CH₃-17), 3.91 (1H, br.s, H_e-10), 4.26 (1H, br.s, H_e-1), 5.07 (1H, dd, J = 11.8, 2.6, H_a-3), 5.55–5.59 (1H, m, H-8), 6.76 (1H, d, J = 5.1, H-13), 7.07 (1H, d, J = 5.1, H-12). ¹³C NMR spectrum (CDCl₃, δ, ppm): 75.43 (d, C-1), 70.22 (d, C-3), 41.51 (t, C-4), 70.85 (s, C-5), 38.15 (d, C-6), 24.50 (t, C-7), 124.03 (d, C-8), 131.75 (s, C-9), 70.50 (d, C-10), 138.24 (s, C-11), 122.88 (d, C-12), 129.96 (d, C-13), 134.20 (s, C-14), 28.34 (q, C-15), 20.71 (q, C-16), 13.73 (q, C-17). Found m/z 294.1279 [M]⁺, C₁₆H₂₂O₃S. Calcd [M]⁺ 294.1284.

2 S ,4 S ( R ),4a R ,8 R ,8a R )-4,7-Dimethyl-2-(5-methylthiophen-2-yl)-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6e). The reaction of 2 (0.300 g, 1.79 mmol) with 5e (0.230 g, 1.83 mmol) in the presence of K10 clay (1.00 g) for 120 min produced a reaction mixture that was treated with CHCl₃. The resulting precipitate was filtered off to afford (S)-6e (0.078 g, 15%). The residue was separated by CC over silica gel to afford an isomeric mixture of (S)- and (R)-6e [(S)–(R) ratio 1.2:1] (0.206 g, 39%). The overall yield of 6e was 54% [(S)–(R) ratio 2.8:1].

( S )-6e. 1H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.49 (3H, s, CH₃-15), 1.76 (1H, ddd, J = 13.3, 2.6, 1.1, H_e-4), 1.79 (3H, m, all J ≤ 2.5, CH₃-16), 1.85 (1H, br.t, J ≈ 8.5, H_a-6), 2.09 (1H, dd, J = 13.3, 12.1, H_a-4), 2.13–2.20 (2H, m, H-7), 2.43 (3H, d, J = 1.1, CH₃-17), 3.81 (1H, dd, J = 2.3, 2.1, H_e-1), 3.82 (1H, br.s, H_e-10), 4.64 (1H, dd, J = 12.1, 2.6, H_a-3), 5.60–5.64 (1H, m, H-8), 6.59 (1H, dq, J = 3.4, 1.1, H-13), 6.78 (1H, d, J = 3.4, H-14). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 79.16 (d, C-1), 74.28 (d, C-3), 42.86 (t, C-4), 71.05 (s, C-5), 39.19 (d, C-6), 23.43 (t, C-7), 125.09 (d, C-8), 131.94 (s, C-9), 70.76 (d, C-10), 143.34 (s, C-11), 140.09 (s, C-12), 125.09 (d, C-13), 124.85 (d, C-14), 27.00 (q, C-15), 20.98 (q, C-16), 15.33 (q, C-17). [α] ²⁶_D –115° (c 3, MeOH). Found m/z 294.1286 [M]⁺, C₁₆H₂₂O₃S. Calcd [M]⁺ 294.1284.

( R )-6e. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.23 (3H, s, CH₃-15), 1.68 (1H, br.t, J δ 8.6, H_a-6), 1.71 (1H, ddd, J = 14.0, 2.6, 1.2, H_e-4), 1.77 (3H, m, all J ≤ 2.5, CH₃-16), 1.88 (1H, dd, J = 14.0, 11.7, H_a-4), 1.94–2.00 (2H, m, H-7), 2.40 (3H, d, J = 1.1, CH₃-17), 3.89 (1H, br.s, H_e-10), 4.22 (1H, dd, J = 2.3, 2.0, H_e-1), 4.93 (1H, dd, J = 11.7, 2.6, H_a-3), 5.52–5.56 (1H, m, H-8), 6.54 (1H, dq, J = 3.4, 1.1, H-13), 6.72 (1H, d, J = 3.4, H-14). ¹³C NMR spectrum (CDCl₃, δ, ppm): 75.35 (d, C-1), 71.78 (d, C-3), 41.47 (t, C-4), 70.76 (s, C-5), 37.97 (d, C-6), 24.38 (t, C-7), 123.99 (d, C-8), 131.64 (s, C-9), 70.39 (d, C-10), 142.98 (s, C-11), 139.07 (s, C-12), 124.29 (d, C-13), 123.73 (d, C-14), 28.21 (q, C-15), 20.72 (q, C-16), 15.13 (q, C-17). Found m/z 294.1286 [M]⁺, C₁₆H₂₂O₃S. Calcd [M]⁺ 294.1284.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-4,7-Dimethyl-2-(5-nitrothiophen-2-yl)-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6f). The reaction of 2 (0.400 g, 2.38 mmol) with 5f (0.370 g, 2.36 mmol) in the presence of K10 clay (1.50 g) for 180 min produced starting diol 2 (0.057 g, 86% conversion of 2), an isomeric mixture of (S)- and (R)-6f [(S)–(R) ratio 1.9:1] (0.115 g, 17%), (S)-6f (0.066 g, 10%), (R)-6f (0.069 g, 11%), and 7 (0.163 g, 26%). The yields were calculated for reacted 2. The overall yield of 6f was 38% [(S)–(R) ratio 1.3:1].

( S )-6f. ¹H NMR spectrum (CD³OD, δ, ppm, J/Hz): 1.53 (3H, d, J = 0.6, CH₃-15), 1.84 (3H, m, all J ≤ 2.5, CH₃-16), 1.88 (1H, ddd, J = 13.2, 3.4, 1.1, H_e-4), 1.88–1.93 (1H, m, H_a-6), 1.94 (1H, ddd, J = 13.2, 11.6, 0.6, H_a-4), 2.09 (1H, ddm, J = 17.7, 10.8, H_a-7), 2.19 (1H, dm, J = 17.7, H_e-7), 3.85 (1H, m, all J < 2.5, H_e-10), 3.87 (1H, dd, J =2.3, 2.1, H_e-1), 4.83 (1H, ddd, J = 11.6, 3.4, 0.9, H_a-3), 5.63–5.67 (1H, m, H-8), 7.01 (1Í, dd, J = 4.2, 0.9, H-14), 7.87 (1H, d, J = 4.2, H-13). ¹³C NMR spectrum (CD3OD, δ, ppm): 79.69 (d, C-1), 74.36 (d, C-3), 43.15 (t, C-4), 71.08 (s, C-5), 39.53 (d, C-6), 23.72 (t, C-7), 125.15 (d, C-8), 132.35 (s, C-9), 71.08 (d, C-10), 156.20 (s, C-11), 151.71 (s, C-12), 129.55 (d, C-13), 123.48 (d, C-14), 26.93 (q, C-15), 21.06 (q, C-16). [α] ²⁶_D –66° (c 11, MeOH). Found m/z 325.0970 [M]⁺, C₁₅H₁₉O₅NS. Calcd [M]⁺ 325.0979.

( R )-6f. ¹H NMR spectrum (CDCl₃, + CD3OD, δ, ppm, J/Hz): 1.17 (3H, s, CH₃-15), 1.64 (1H, ddm, J = 10.8, 6.6, H_a-6), 1.68 (1H, dd, J = 14.0, 11.0, H_a-4), 1.73 (1H, ddd, J = 14.0, 3.5, 1.1, H_e-4), 1.75 (3H, br.s, CH₃-16), 1.81 (1H, ddm, J = 17.7, 10.8, H_a-7), 1.95 (1H, dddm, J = 17.7, 6.6, 5.2, H_e-7), 3.81 (1H, br.s, H_e-10), 4.17 (1H, br.t, J_1e,10e ≈ J_1e,6a ≈ 2.2, H_e-1), 4.95 (1H, ddd, J = 11.0, 3.5, 0.7, H_a-3), 5.48–5.52 (1H, m, H-8), 6.77 (1H, dd, J = 4.2, 0.7, H-14), 7.69 (1H, d, J = 4.2, H-13). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 75.54 (d, C-1), 71.71 (d, C-3), 41.15 (t, C-4), 69.88 (s, C-5), 37.50 (d, C-6), 24.16 (t, C-7), 123.46 (d, C-8), 131.51 (s, C-9), 69.80 (d, C-10), 155.45 (s, C-11), 150.26 (s, C-12), 128.24 (d, C-13), 121.70 (d, C-14), 27.58 (q, C-15), 20.48 (q, C-16). [α] ²⁶_D –1° (c 5, MeOH). Found m/z 325.0970 [M]⁺, C₁₅H₁₉O₅NS. Calcd [M]⁺ 325.0979.

Compound 7. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.83 (3H, m, all J ≤ 2.5, CH₃-16), 1.96 (1H, dddq, J = 17.8, 6.7, 5.4, 1.4, H_e-7), 2.23 (1H, ddm, J = 17.8, 10.8, H_a-7), 2.48 (1H, dd, J = 14.0, 3.5, H_e-4), 2.50–2.58 (2H, m, H_a-4, 6), 3.74 (1H, br.dd, J_1e,6a ≈ J_1e,10e ≈ 2.2, H_e-1), 3.91 (1H, br.s, H_e-10), 4.60 (1H, ddd, J = 11.0, 3.5, 0.8, H_a-3), 4.87 (1H, m, all J ≤ 2.2, H-15), 4.96 (1H, m, all J ≤ 2.2, H-15′), 5.58–5.61 (1H, m, H-8), 6.85 (1H, dd, J = 4.2, 0.8, H-14), 7.76 (1H, d, J = 4.2, H-13). ¹³C NMR spectrum (CDCl₃, δ, ppm): 80.71 (d, C-1), 75.95 (d, C-3), 37.93 (t, C-4), 144.59 (s, C-5), 36.39 (d, C-6), 25.89 (t, C-7), 124.23 (d, C-8), 131.27 (s, C-9), 69.97 (d, C-10), 154.10 (s, C-11), 150.76 (s, C-12), 128.13 (d, C-13), 121.95 (d, C-14), 111.31 (t, C-15), 20.77 (q, C-16). Found m/z 307.1755 [M]⁺, C₁₅H₁₇NO₄S. Calcd [M]⁺ 307.1748.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-2-(4,5-Dibromothiophen-2-yl)-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (6g). The reaction of 2 (0.190 g, 1.13 mmol) with 5g (0.200 g, 0.75 mmol) in the presence of K10 clay (0.80 g) for 24 h produced 6g [(S)–(R) ratio 2:1] (0.080 g, 32%), 8 (0.048 g, 20%), 9 (0.048 g, 19%), and 2 (0.095 g, 50% conversion of 2). Recrystallization from CHCl₃ of the isomeric mixture of (S)- and (R)-6g produced (S)-6g. Yields were calculated for reacted diol 2.

( S )-6g. ¹H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.47 (3H, d, J = 0.7, CH₃-15), 1.76 (1H, ddd, J = 13.2, 2.8, 1.1, H_e-4), 1.80 (3H, m, all J ≤ 2.5, CH₃-16), 1.84 (1H, ddm, J = 10.6, 6.5, other J < 2.5, H_a-6), 1.96 (1H, dd, J = 13.2, 12.0, H_a-4), 2.06 (1H, dddqd, J = 18.3, 10.6, 2.5, 1.5, H_a-7), 2.15 (1H, dddq, J = 18.3, 6.5, 5.2, 1.5, H_a-7), 3.79 (1H, dd, J = 2.3, 2.1, H_e-1), 3.82 (1H, br.s, H_e-10), 4.61 (1H, ddd, J = 12.0, 2.8, 1.0, H_a-3), 5.59–5.63 (1H, m, H-8), 6.80 (1H, d, J = 1.0, H-14). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 78.91 (d, C-1), 73.56 (d, C-3), 42.01 (t, C-4), 70.60 (s, C-5), 38.78 (d, C-6), 23.08 (t, C-7), 124.78 (d, C-8), 131.61 (s, C-9), 70.41 (d, C-10), 147.45 (s, C-11), 110.68 and 113.27 (2s, C-12, C-13), 126.69 (d, C-14), 26.79 (q, C-15), 20.89 (q, C-16). [α] ²⁴_D –72° (c 2, MeOH). Found m/z 435.9341 [M]⁺, C₁₅H₁₈Br₂O₃S. Calcd [M]⁺ 435.9338.

( R )-6g. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.25 (3H, s, CH₃-15), 1.66 (1H, ddm, J = 11.2, 6.5, H_a-6), 1.72 (1H, ddd, J = 14.0, 3.0, 1.2, H_e-4), 1.76–1.82 (1H, m, H_a-4), 1.80 (3H, m, all J 2.5, CH₃-16), 1.85–2.05 (2H, m, H-7), 3.90 (1H, br.s, H_e-10), 4.22 (1H, br.dd, J_1e,10e ≈ J_1e,6a ≈ 2.2, H_e-1), 4.91 (1H, ddd, J₃ = 11.3, 3.0, 0.8, H_a-3), 5.54–5.57 (1H, m, H-8), 6.72 (1H, d, J = 0.8, H-14). ¹³C NMR spectrum (CDCl₃, δ, ppm): 75.38 (d, C-1), 71.55 (d, C-3), 41.07 (t, C-4), 70.62 (s, C-5), 38.09 (d, C-6), 24.36 (t, C-7), 123.88 (d, C-8), 131.68 (s, C-9), 70.28 (d, C-10), 147.09 (s, C-11), 111.16 and 112.31 (2s, C-12, C-13), 125.83 (d, C-14), 28.31 (q, C-15), 20.72 (q, C-16). Found m/z 435.9341 [M]⁺, C₁₅H₁₈Br₂O₃S. Calcd [M]⁺ 435.9338.

Compound 8. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.81 (3H, m, all J ≤ 2.5, CH₃-16), 1.95 (1H, dddq, J = 18.1, 6.6, 5.3, 1.5, H_e-7), 2.24 (1H, dddqd, J = 18.1, 10.8, 2.5, 1.6, H_a-7), 2.41 (1H, dd, J = 13.9, 3.0, H_e-4), 2.50–2.58 (2H, m, H_a-4, 6), 3.71 (1H, dd, J = 2.2, 2.2, H_e-1), 3.89 (1H, br.s, H_e-10), 4.50 (1H, ddd, J = 11.5, 3.0, 1.0, H_a-3), 4.84 (1H, dd, J = 2.0, 1.8, H-15), 4.94 (1H, dd, J = 2.0, 1.8, H-15′), 5.58–5.61 (1H, m, H-8), 6.77 (1H, d, J = 1.0, H-14). ¹³C NMR spectrum (CDCl₃, δ, ppm): 80.59 (d, C-1), 75.92 (d, C-3), 37.65 (t, C-4), 146.51 (s, C-5), 36.52 (d, C-6), 25.98 (t, C-7), 124.41 (d, C-8), 131.29 (s, C-9), 70.12 (d, C-10), 145.12 (s, C-11), 110.38 and 112.85 (2s, C-12, C-13), 126.00 (d, C-14), 110.98 (t, C-15), 20.82 (q, C-16). [α] ²⁴_D –16° (c 2, CHCl₃). Found m/z 417.9230 [M]⁺, C₁₅H₁₆Br₂O₂S. Calcd [M]⁺ 417.9232.

Compound 9. ¹H NMR spectrum (CDCl₃, δ, ppm, J/Hz): 1.23 (3H, s, CH₃-16), 1.47 (3H, s, CH₃-15), 1.50 (1H, ddd, J = 10.8, 6.1, 1.9, H_a-6), 1.79 (3H, m, all J < 2.6, CH₃-17), 2.04 (1H, dddq, J = 17.9, 6.1, 5.3, 1.5, H_e-7), 2.34 (1H, dddqd, J = 17.9, 10.8, J_7a,8 = J_7a,17 = 2.5, 1.6, H_a-7), 3.86 (1H, br.s, H_e-10), 4.30 (1H, dd, J = 2.3, 1.9, H_e-1), 5.61–5.64 (1H, m, H-8), 5.90 (1H, d, J = 0.7, H-3), 6.90 (1H, d, J = 1.0, H-14). ¹³C NMR spectrum (CDCl₃, δ, ppm): 74.98 (d, C-1), 91.65 (d, C-3), 75.50 (s, C-5), 33.88 (d, C-6), 22.79 (t, C-7), 125.29 (d, C-8), 130.58 (s, C-9), 70.24 (d, C-10), 143.37 (s, C-11), 111.64 and 112.80 (2s, C-12, C-13), 127.57 (d, C-14), 22.58 (q, C-15), 26.96 (q, C-16), 20.46 (q, C-17). [α] ²⁴_D –36° (c 4, CHCl₃). Found m/z 435.9330 [M]⁺, C₁₅H₁₈Br₂O₃S. Calcd [M]⁺ 435.9338.

(2 S ,4 S ( R ),4a R ,8 R ,8a R )-4,7-Dimethyl-2-(thiophen-3-yl)-3,4,4a,5,8,8a-hexahydro-2 H -chromen-4,8-diol (11). The reaction of 2 (0.300 g, 1.79 mmol) with 10 (0.200 g, 1.79 mmol) in the presence of K10 clay (1.00 g) for 60 min produced starting diol 2 (0.070 g, 77% conversion of 2) and 11 (0.205 g, 54% calculated for reacted diol 2) [(S)–(R) ratio 1.4:1].

( S )-11. ¹H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.51 (3H, d, J = 0.7, CH₃-15), 1.72 (1H, ddd, J = 13.3, 2.6, 1.2, H_e-4), 1.80 (3H, m, all J ≤ 2.5, CH₃-16), 1.87 (1H, br.t, J = 8.9, H_a-6), 2.02 (1H, dd, J = 13.3, 12.1, H_a-4), 2.14–2.19 (2H, m, H-7), 3.82 (1H, dd, J = 2.4, 2.1, H_e-1), 3.84 (1H, br.s, H_e-10), 4.59 (1H, dd, J = 12.1, 2.6, H_a-3), 5.62–5.65 (1H, m, H-8), 7.07 (1H, dd, J = 5.0, 1.3, H-14), 7.24 (1H, ddd, J = 3.0, 1.3, 0.7, H-12), 7.30 (1H, dd, J = 5.0, 3.0, H-13). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 79.03 (d, C-1), 74.64 (d, C-3), 42.32 (t, C-4), 71.11 (s, C-5), 39.21 (d, C-6), 23.50 (t, C-7), 125.12 (d, C-8), 131.98 (s, C-9), 70.80 (d, C-10), 143.96 (s, C-11), 121.78 (d, C-12), 126.28 (d, C-13), 126.66 (d, C-14), 27.00 (q, C-15), 21.02 (q, C-16). Found m/z 280.1130 [M]⁺, C¹⁵H²⁰O³S. Calcd [M]⁺ 280.1128.

( R )-11. ¹H NMR spectrum (CDCl₃ + CD₃OD, δ, ppm, J/Hz): 1.15 (3H, s, CH₃-15), 1.58–1.67 (2H, m, H_e-4, H_a-6), 1.72 (3H, m, all J ≤ 2.5, CH₃-16), 1.73 (1H, dd, J = 14.0, 11.8, H_a-4), 1.87–1.94 (2H, m, H-7), 3.81 (1H, br.s, H_e-10), 4.13 (1H, dd, J = 2.4, 2.1, H_e-1), 4.80 (1H, dd, J = 11.8, 2.6, H_a-3), 5.48–5.51 (1H, m, H-8), 6.97 (1H, dd, J = 5.0, 1.3, H-14), 7.10 (1H, ddd, J = 3.0, 1.3, 0.7, H-12), 7.17 (1H, dd, J = 5.0, 3.0, H-13). ¹³C NMR spectrum (CDCl₃ + CD₃OD, δ, ppm): 75.27 (d, C-1), 72.11 (d, C-3), 40.79 (t, C-4), 70.15 (s, C-5), 37.68 (d, C-6), 24.31 (t, C-7), 123.66 (d, C-8), 131.63 (s, C-9), 70.02 (d, C-10), 143.50 (s, C-11), 120.58 (d, C-12), 125.38 (d, C-13), 125.74 (d, C-14), 27.74 (q, C-15), 20.50 (q, C-16). Found m/z 280.1130 [M]⁺, C₁₅H₂₀O₃S. Calcd [M]⁺ 280.1128.

Analgesic Activity. All experiments were conducted using laboratory male mice (22–25 g). Test groups consisted of eight animals each. Tested agents were injected intragastrically at a dose of 10 mg/kg as aqueous Tween suspensions one hour before inducing the model. Control animals were injected with the corresponding solvent.

The acetic-writhing test was induced by i.p. injection of AcOH (0.75%, 0.1 mL/10 g of body mass). The degree of the pain reaction was assessed 5 min after AcOH injection from the number of convulsions of each animal in 3 min.

The hot-plate test placed animals on a metallic surface heated to 54 ± 0.5°C that was surrounded by a transparent cylinder. The latent time of the pain reaction (licking hind paws or rearing) in seconds was recorded for each animal.

The studied agents of general formulas 6 and 11 were injected without separating diastereomers. Table 1 presents the results. Statistical processing used the Statistica 8.0 software.