Introduction

Cancer is still one of the most fatal diseases, affecting nearly 7 million persons per year all over the world. It is characterized by loss of cell growth control causing a cellular mass called cancer [1,2,3,4,5,6]. However, death is most often accompanies cancer because of metastasis which is responsible for spreading cancer to another part in the body to establish secondary cancerous growths [7,8,9,10,11,12]. It was found that strategies for cancer treatment such as surgery and radiation cannot control the spread of tumor; so many scientific trials to treat cancer had been depending on conventional chemotherapy [13,14,15,16]. Unfortunately, the conventional chemotherapy did not differentiate between the normal human cells and affected cells, causing many drawbacks [17, 18]. Consequently, to circumvent these drawbacks a new strategy for cancer treatment compromising the use of selective tumor drugs called molecular targeted therapies which inhibits certain receptors and signaling pathways which stimulate tumor cell growth had been developed [19,20,21,22]. Protein kinases (PKs) are enzymes that stimulate phosphate transfer from ATP to amino acids tyrosine, serine and/ or threonine residues in protein substrates [23,24,25,26]. Also, PKs are important enzymes responsible for cellular signaling processes such as cell growth regulation, differentiation, migration, and metabolism [27,28,29]. Mutation or overexpression of many PKs had been reported in multiple human cancers [30,31,32,33]. Consequently, inhibiting protein kinase has been used as a selective way for targeting cancer cells [34,35,36,37,38]. The literature survey explained that the binding site of kinase inhibitor consists of five essential regions; adenine-binding site, sugar region, phosphate-binding region (hydrophilic channel), hydrophobic region I and hydrophobic region II [39, 40]. Most discovered kinase inhibitors should be small molecules and ATP-competitive inhibitors that exhibited up to three hydrogen bonding interactions with the amino acids present in the target kinase [41,42,43].

Pyrimidine ring attracted much attention due to its diverse array of biological and pharmacological activities especially anticancer activity [44,45,46,47,48,49]. Many fused pyrimidine derivatives exerted their anticancer activity through inhibiting many types of PKs as they are considered as bioisosteres to purine scaffold from which ATP is formed [12, 50,51,52,53]. Herein, this review reveals the new approaches and medicinal chemistry efforts in search for new pyrimidine and fused pyrimidine scaffolds as PKs inhibitors.

Pyrimidine derivatives

At the beginning of the twenty-first century, scientist’s efforts discovered more potent and selective tyrosine kinase inhibitors, imatinib (GleevecTM) (1) [54, 55], nilotinib (TasignaTM) (2) [56, 57], and dasatinib (SpryclTM) (3) [58, 59] (Fig. 1). FDA approved these pyrimidine derivatives for treating chronic myelogenous leukemia via inhibiting Bcr-Abl tyrosine kinases [60,61,62].

Fig. 1
figure 1

Chemical structure of tyrosine kinase inhibitors imatinib (1), nilotinib(2) and dasatinib (3)

Full size image

In 2013, a group of investigators designed and synthesized a new series of pyrimidine derivatives as anaplastic lymphoma kinase (ALK) inhibitors with antiproliferative potential against H3122 [63]. From this series, compound 9 (IC50 = 0.004 µM, IC50 = 0.034 µM in cell based assay) exhibited 2.5-fold better ALK inhibitory activity and antiproliferative potential than the reference compound crizotinib (IC50 = 0.01 µM in ALK assay, IC50 = 0.092 µM in cell based assay) (10). SAR study revealing the effect of various substituents is illustrated in Fig. 2.

Fig. 2
figure 2

SAR of pyrimidine derivatives asALK inhibitor, chemical structure of derivative(9) and crizotinib (10)

Full size image

The target compound 9 was obtained in 75% yield by reacting compound 4 with 4-(N-Boc-piperazin-1-yl)-2-methoxyaniline 5 in the presence of diisopropylethylamine, followed by separating the obtained regioisomers (6&7) and reacting compound 6 with trimethoxy aniline (Scheme 1).

Scheme 1
scheme 1

Synthesis of ALK inhibitor (9)

Full size image

In 2020, Xu et al. [64] designed and constructed novel 2,4-disubstitutedpyrimidines as Aurora kinase inhibitors. In addition, the prepared derivatives were evaluated for their activity toward A549, HCT-116, and MCF-7 cell lines and SAR of the designed derivatives are depicted in Fig. 3. From these constructed derivatives, compound 11 demonstrated similar antitumor potential (IC50 equal to 12.05, 1.31, and 20.53 µM toward A549, HCT-116, and MCF-7, respectively) to that recorded by the standard VX680 (IC50 = 3.9, 1.49, and 17.39 µM, respectively). Regarding Aurora suppression activity, this derivative demonstrated suppression potential toward Aurora A (IC50 = 79.4 µM) and Aurora B (IC50 = 66.3 µM). SAR studies showed that cyclohexyl moiety at the tail exhibited better antiproliferative than aromatic ring toward HCT-116 cell lines. Replacing NH on the urea group with CH2 did not affect the anticancer activity on the tested three cell lines.

Fig. 3
figure 3

SAR of some novel pyrimidine derivatives and chemical structure of target pyrimidine 11 as Aurora A and Aurora B inhibitor

Full size image

Furthermore, the N-(4-(2-(4-(morpholinophenyl)amino)pyrimidin-4-yl)phenyl)acrylamide derivative 12 (Fig. 4) was newly synthesized and showed high JAK3 suppression activity with IC50 = 1.7 nM with higher selectivity than JAK2 and JAK1 [65]. This selectivity was attributed to the formation of hydrophobic interaction between the aromatic amine moiety and Leu828 and Gly908 amino acids. Moreover, this candidate 12 demonstrated better suppression of T-cell proliferation potential (IC50 = 0.83 µM) than exhibited by tofacitinib (IC50 = 1.38 µM). SAR study revealing the effect of various substituents is illustrated in Fig. 4. In addition, the benzoxazolopyrimidine derivative 13 (Fig. 4) showed excellent anticancer potential toward leukemia cell line (RPMI-8226), prostate cancer cell line (PC-3), and renal cancer cell line (A498) with IC50 = 0.72, 0.7932, and 0.8511 µM, respectively. The mechanism of anticancer potential of this candidate was suggested to be PTK inhibition on MDA-MB-468 cell lines with IC50 = 0.07 µM [66].

Fig. 4
figure 4

Chemical structures of pyrimidines 12 and 13

Full size image

VX680 (14) (Fig. 5) is a small pyrimidine heterocycle reported to suppress Aurora kinases A, B, and C with ki equal to 0.6, 18, and 4.6 nµ, sequentially [67]. This compound 14 has the ability to inhibit many cancer types as ovarian cancer, colon cancer, and leukemia [68]. While, ENMD-2076 (15) suppress Aurora A selectively with IC50 = 14 nM [69]. Luo et al. [70] designed and prepared new C-2, C-4, C-6 trisubstitutedpyrimidines as Aurora A suppressor. The design of these pyrimidine targets was based upon some modifications of both VX680 and ENMD-2076. These modifications include introducing N-substituted aniline at C-2 instead of S-substituted moiety in VX680. In addition, modification included replacement of styrene side chain in ENMD-2076 with N-benzylamine. SAR explaining effect of substituent at C-6 on the inhibitory potential on Aurora A is appeared in Fig. 5. From the constructed pyrimidines compound 16 recorded potential inhibitory effect on aurora A with IC50 = 25 nM through hydrophobic interaction and three hydrogen bondings with K162, A213, and L139. Moreover, the designed derivatives were assayed for anticancer potential in vitro by the use of VX680 as a standard toward breast cancer cell line as MCF-7, SK-BR-3, MDA-MD-231, and leukemia cell lines as K-562, U937, HL-60, MOLT-4. Results of compounds 16 and 17 are explained in Fig. 5.

Fig. 5
figure 5

SAR of some novel pyrimidine derivatives and chemical structure of VX680, ENMD-2076 and target pyrimidine 16, 17, and 18 as Aurora kinase inhibitors

Full size image

Long et al. [71] in 2018 revealed that the disubstituted anilino moiety at C-2 of pyrimidine nucleus showed higher Aurora A inhibitory potential than the monosubstituted anilino fragment. This is obvious upon comparing compound 18 (IC50 = 7.7 nM) with 4-aminobenzoate 17 (IC50 = 46 nM).

Recently, in 2019, novel series of 4,6-diaryl-2-amine derivatives were evaluated for their anticancer potential toward colon cancer cell line (HCT-116) [72]. All the new compounds showed anticancer activity with half maximal cell growth inhibitory concentrations equal to 1.45–40.82 µM. The candidate 19—the most active anticancer agent (GI50 = 1.45)—was subjected to kinase assay using 25 cancer-associated kinases applying EMD Millipore Kinase Profiler service assay protocol. This tested compound 19 recorded high selectivity toward Aurora A kinase than other tested kinases. In silico docking of this derivative demonstrated that this derivative performed two hydrogen bondings with Ala213 and Pro214, in addition to seven hydrophobic interactions (Leu263, Arg220, Gly216, Tyr212, Glu211, Leu139, and Arg137) as seen in Fig. 6.

Fig. 6
figure 6

Chemical structure of compound 19 and its binding mode of compound 19 within Aurora A kinase

Full size image

Pyrazolo[3,4-d]pyrimidine derivatives

Pyrazolopyrimidine derivatives 1NA-PP1 (20) and 1NM-PP1 (21) (Fig. 7) were documented to inhibit Src kinase and widely reported as standards for design of many pyrazolo[3,4-d]pyrimidine derivatives [73,74,75].

Fig. 7
figure 7

Chemical structures of 1NM-PP1 (20) and 1NM-PP1 (21)

Full size image

Moreover, novel derivatives of 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines were designed based upon some chemical modifications of olomoucine 26 and roscovitine 27. These chemical modifications include replacing the imidazole ring in olomoucine with a pyrazole ring in addition to introduction different substituents at C-4, C-6, and N-1 of pyrazolopyrimidine. The newly synthesized derivatives were evaluated for their inhibitory activity against CDK2 and for their antiproliferative potential against A431, SNU638, and HCT-116 cell lines. In general, structure–activity relationship (SAR) recorded that compounds having anilino group at C-4 showed higher CDK2 and cell division than 4-benzyl derivatives. Compounds 25a, b having a 3-fluoroaniline group at C-4 were prepared and revealed comparable or superior cyclin-dependent kinase 2 (CDK2) (IC50 = 0.5 µM for 33a, 0.7 µM for 33b), inhibitory activity to those of olomoucine 26 (IC50 = 7 µM) and roscovitine 27 (IC50 = 0.5 µM) as reference compounds [76]. Moreover, unsubstitution at N-1 recorded higher potency for CDK2 inhibitory effect than substituted analogs. Regarding substitution at C-6, it was found that no difference between monoethanolamine and diethanolamine toward CDK2 activity (Fig. 8). The pyrazolopyrimidine derivatives (25a,b) were prepared as illustrated in Scheme 2. Accordingly, the reaction of 4-chloro-6-methylmercaptopyrazolo[3,4-d]pyrimidine (22) with 3-fluoroaniline in the presence of Hunig’s base in n-butanol yielded compound 23 which upon oxidation with m-CPBA followed by nucleophilic displacement of the resulting activated methylsulfonyl groups with hydroxylamines gave the target 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines 25a,b.

Fig. 8
figure 8

Chemical structures of compounds (25a,b), olomoucine (26) and roscovitine (27)

Full size image
Scheme 2
scheme 2

Synthesis of 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines 25a,b

Full size image

Some 4-aminopyrazolo[3,4-d]pyrimidines substituted at position 1 and 6 were prepared and exhibited anticancer activity toward A431 cells, inhibited Src phosphorylation and induced apoptotic cell death. SAR studies of these derivatives are explained in Fig. 9. From the prepared compounds, derivative 26 incorporating a methylthio moiety at position 6 inhibited Src phosphorylation than the reference compound 27 (Fig. 9), so, the size of the alkyl group at position 6 was essential for activity [77].

Fig. 9
figure 9

Chemical structures of 1,4-disubstitutedpyrazolo[3,4-d]pyrimidine derivatives (26) and (27)

Full size image

Recently, novel derivatives of 4,6-disubstituted pyrazolopyrimidines incorporating various anilines at C-4 and thiophenethyl or thiopentane moieties at C-6 had been synthesized [78]. All the synthesized compounds were evaluated for in vitro CDK2/cyclin E and Abl kinase inhibitory activity as well as antiproliferative activity against K-562 (chronic myelogeneous leukemia), and MCF-7 (breast adenocarcinoma) cell lines. The SAR studies are explained in Fig. 10. From SAR, it is clear that derivative with thiophenethyl at C-6 with monosubstituted aniline showed better CDK2 inhibitory potential than thiopentane at C-6 and disubstituted anilines. From the prepared derivatives, compound 28 was the most CDK inhibitor with IC50 = 5.1 µM with antiproliferative activity toward K-562 (chronic myelogeneous leukemia), and MCF-7 (breast adenocarcinoma) cell lines with IC50 = 24.6 and 24.3 µM, respectively.

Fig. 10
figure 10

SAR of pyrazolopyrimidine derivatives as CDK2 inhibitor and chemical structure of compound 28

Full size image

In 2008, new derivatives of 4-aminosubstitutedpyrazolo[3,4-d]pyrimidines were prepared and exhibited inhibitory activity against Src and proto-oncogene tyrosine protein kinase Ab1 kinases [79]. From this series, compound 29 was docked within adenine triphosphate (ATP)-binding sites of the two target enzymes (Fig. 11). This study recorded that in both enzymes compound 29 located pyrazolopyrimidine nucleus into the adenine region of the ATP-binding site, introducing the side chains at C-4 and N-1 toward two hydrophobic regions and the alkylthio substituent toward the external region of the binding pocket. Furthermore, this target compound performed two hydrogen bonding interactions with Src enzyme and one hydrogen bonding interaction with Abl as shown below (Fig. 11).

Fig. 11
figure 11

A Binding of compound 29 into ATP-binding site of Src enzyme. B Binding of compound 29 into ATP-binding site of Ab1 enzyme

Full size image

Ducray et al. [80] reported the preparation and in vitro evaluation of a new group containing anilinopyrazolo[3,4-d]pyrimidine derivatives 30a–c (Fig. 12) as receptor tyrosine protein kinase erb-2 (erbB2) and EGFR kinase inhibitors. Encouraging results with compound 30c provided potent, orally active erbB2 kinase inhibitor in rats and dogs with IC50 = 0.001 µM toward erbB2. Furthermore, novel derivatives of pyrazolo[3,4-d]pyrimdine-3,6-diamines (Fig. 12) were synthesized as potent and selective non-receptor tyrosine kinase, activated Cdc42Hs-asociated Kinase1 (ACK1) inhibitors. Compounds 31a and 31b showed promising ACK1 suppression with IC50 = 0.02 µM and 0.04 µM. A brief description SAR is illustrated in Fig. 12 [81].

Fig. 12
figure 12

Chemical structures of some pyrazolo[3,4-d]pyrimidines (30a–c) and (31a,b)

Full size image

Moreover, compound 32 (Fig. 13) was identified to inhibit EGFR enzyme at low-micromolar concentration with antiproliferative effect against cancer cells [82]. The in silico docking study of compound 32 demonstrated that the amino H and N-5 of pyrimidine ring make hydrogen bonds with backbone atoms of M769. The interaction of the ligand with T766 is mediated by a water molecule, and the 3-methylphenyl moiety substituted at N(1) is buried within the binding pocket (Fig. 13).

Fig. 13
figure 13

Chemical structures of pyrazolo[3,4-d]pyrimidine derivative (32)and its binding mode within EGFR

Full size image

Recently in 2016, a new series of pyrazolo[3,4-d]pyrimidines hybridized with (4-substitutedbenzylidene)acetohydrazide derivatives (33a–g) and (Fig. 14) were synthesized and evaluated for their inhibitory activity toward epidermal growth factor receptor tyrosine kinase (EGFR-TK) [83]. Among these targets 33a–g, 33g was the most potent EGFR inhibitor (IC50 = 4.18 μM) followed by compound 33c (IC50 = 4.72 μM). Pyrazolo[3,4-d]pyrimidine combined with pyrazole moiety (35) revealed antiproliferative activity with IC50 = 5.00–32.52 μM on breast (MCF-7), colon (HCT-116), and liver (HEPG2) cancer cell lines [84]. Furthermore, this studied candidate inhibited fibroblast growth factor receptor (FGFR) with IC50 = 5.18 μM.

Fig. 14
figure 14

Chemical structures of some pyrazolo[3,4-d]pyrimidine derivatives (33a–g) and (35) as EGFR and FGFR kinase inhibitors

Full size image

The [4-(1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4-ylamino)phenyl]methanone derivative (35) was synthesized by heating 4-(1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4-ylamino)benzohydrazide (34) with acetylacetone in acetic acid for 10 h under reflux conditions, as shown in Scheme 3.

Scheme 3
scheme 3

Synthesis of pyrazolo[3,4-d]pyrimidine derivative (35)

Full size image

Pyrido[2,3-d]pyrimidine derivatives

Two decades ago, PD 089828 (36) was synthesized as a novel 6-aryl-pyrido[2,3-d]pyrimidine derivative (Fig. 15), which was discovered as inhibitor for many PKs as human full-length fibroblast growth factor receptor-1 (FGFR-1), platelet-derived growth factor (PDGF) receptor b subunit (PDGFR-b), Src nonreceptor tyrosine kinase (c-Src), and epidermal growth factor receptor (EGFR) [85]. In addition, another group of pyrido[2,3-d]pyrimidines (37a–d) (Fig. 15) had been prepared and assessed for their potential antitumor agents. These compounds showed ATP-competitive inhibition of c-Src kinase with IC50 values 10 nM and from 6 to 100-folds selectivity for c-Src tyrosine kinase relative to the basic fibroblast growth factor receptor (bFGFr) tyrosine kinase, platelet-derived growth factor receptor (PDGFr) tyrosine kinase, and epidermal growth factor receptor (EGFr) tyrosine kinase [86, 87]. Moreover, the pyridopyrimidine derivative (PD 180970, 38) (Fig. 15) was prepared by Kraker et al. [87] and subjected to biological evaluation, which revealed that they inhibit Gab2 tyrosine phosphorylation in K-562 cells.

Fig. 15
figure 15

Chemical structures of some pyrido[2,3-d]pyrimidine derivatives PD 089828 (36), 37a–d, and PD 180970 (38)

Full size image

A group of coworkers [88] synthesized a novel series of pyrido[2,3-d]pyrimidine derivatives 39a–l (Fig. 16) as tyrosine kinase inhibitors. From this series, PD 089828 (39b) exhibited highly inhibitory activity against PDGFr, FGFr, and c-Src tyrosine kinase with IC50 values of 1.25, 0.14, and 0.22 µM, respectively. A SAR study was performed to reveal the effect of phenyl substitution at the 6-position on the potency of these three kinases. This study ascertained the importance of the presence of phenyl moieties in the 6-position substituted with either halogen or methyl groups at 2- and/or 6-position of phenyl ring on the inhibitory activity against PDGFr, FGFr, and c-Src tyrosine kinase as in the target compounds (39c, 39d, and 39f) which showed inhibitory activity than the unsubstituted parent compound 39a. Moreover, this study recorded that the introduction of ethyl (39i), or methoxy (39j) in the 2-position of the phenyl ring resulted in a decreased the inhibitory activity against both PDGFr-TK and FGFr-TK but c-Src inhibitory activity is not affected. In addition, this work explained that compounds which substituted at 4-position of the phenyl ring such as 39e, 39k, and 39l exhibited marked decrease or loss in their inhibitory activity against all tested kinases. Furthermore, the 2,4,6-trimethyl derivative 39h exhibited the same inhibitory activity as the 2,6-dimethyl derivative 39f, even though it contained a methyl substituent in the 4-position. Furthermore, the 3,5-dimethyl derivative 39g displayed selectivity for the FGFr-TK relative to the PDGFr-TK and the c-Src tyrosine kinase.

Fig. 16
figure 16

Chemical structures of 6-phenylpyrido[2,3-d]pyrimidine derivatives (39a–l)

Full size image

In an attempt to design potent kinase inhibitors, Reddy et al. [89] tested more than 150 cyanopyrido[2,3- d]pyrimidine derivatives. They found pyrido[2,3-d]pyrimidine-6-carbonitrile derivative (40) (Fig. 17) revealed the most potent activity and the most apoptosis inducer in tumor cells at a concentration of 30–100 nM. Moreover, this target compound inhibited many kinases such as CDK4/CYCLIN D1 and ARK5 kinases. Furthermore, Edupugantiet al. [90] reported the design and synthesis of a novel series of pyrido[2,3-d]pyrimidine-2,4-dione derivatives, which were evaluated for the eukaryotic elongation factor-2 kinase (eEF-2K) inhibitory activity. This study reported that compounds 43 (IC50 = 420 nM) and 44 (IC50 = 930 nM) (Fig. 17) were found to be the most active compounds among all the tested compounds.

Fig. 17
figure 17

Chemical structures of pyrido[2,3-d]pyrimidine-7-one derivative (40) and pyrido[2,3-d]pyrimidine-2,4-dione derivatives (43 and 44)

Full size image

The in silico docking studies of derivatives 43 within Eef-2k is shown in Fig. 18. The binding of inhibitor 6 involves hydrogen bonds to residues K170, I232, and G234. The hydrophobic cyclopropyl and ethyl groups are buried deep inside the adenine-binding pocket and underneath the Gly-rich-loop, respectively.

Fig. 18
figure 18

Binding of compound 43 within eEF-2K active site

Full size image

Synthesis of pyrido[2,3-d]pyrimidine-2,4-dione derivatives 43 and 44 were demonstrated in Scheme 4. The uracil derivatives 41a,b was subjected to Vilsmeierreactionto give the intermediate derivative 42, which then was treated with triethylamine and cyanoacetamide in ethanol, to afford the target compounds 43 and 44.

Scheme 4
scheme 4

Synthesis of pyrido[2,3-d]pyrimidine derivatives 43 and 44

Full size image

A novel 4-aminopyrido[2,3-d]pyrimidine derivative 45 (Fig. 19) was recorded to inhibit tyrosine kinases in the B-cell receptor and demonstrated antiproliferative activity toward 20 non-Hodgkin’s lymphomas (NHLs) cell lines with GI50 ranging from 1.3 to 6.9 μM at 24 h, and 1.4 to 7.2 μM at 48 h [83]. Also, a novel series of oxopyrido[2,3-d]pyrimidines was prepared and it was found that they inhibit gefitinib-resistant EGFRL858R, T790M with 100-fold selectivity over wild type. From this group, compound 46 (Fig. 19) showed strong antiproliferative activity against H1975 nonsmall cell lung cancer cell line, the first line mutant HCC827 cell line, and showed also promising antitumor activity in an EGFRL858R,T790M driven H1975 xenograft model sparing the side effects associated with the inhibition of wild-type EGFR [84].

Fig. 19
figure 19

Chemical structures of some pyrido[2,3-d]pyrimidine derivatives (45, 46)

Full size image

Quinazoline derivatives

A new series of quinazoline derivatives was synthesized as EGFR kinase inhibitors and evaluated in cancer clinical trials. The anilinoquinazoline-containing compounds, Erlotinib (TarcevaTM) (47) [91, 92] and gefitinib (IressaTM) (48) [93, 94], had been used for the treatment of patients with advanced nonsmall lung cancer. In addition, lapatinib (TykerbTM) (49) was used for the treatment of human epidermal growth factor receptor 2 (HER2) positive advanced or metastatic breast cancer [95,96,97] (Fig. 20).

Fig. 20
figure 20

Chemical structures of some anilinoquinazoline derivatives erlotinib (47), gefitinib (48) and lapatinib (49)

Full size image

Another series of 4-anilinoquinazoline derivatives was prepared and tested for their inhibitory activity toward EGFR tyrosine kinase. SAR performed on this series recorded that substitution on the three position of aniline moiety with small lipophilic electron withdrawing group led to an increase in the potency of quinazoline derivative (50) (Fig. 21), which showed EGFR inhibitory activity with IC50 = 0.029 nM [98]. Moreover, compound 51 (Fig. 21) was synthesized and exhibited inhibitory activity toward both c-Src and Abl kinases [99].

Fig. 21
figure 21

Chemical structures of some 4-substituted-quinazoline derivatives (50) and (51)

Full size image

A new series of 5-aminopyrimidinylquinazolines 52a–e (Fig. 22) had been designed as specific Aurora kinase inhibitors by Heron et al. [100]. The SAR study showed that the potency was dependent on the substitution on the phenyl ring of the benzamido group. The activity was increased by adding small hydrophobic groups such as 3-chloro (52a) and the 3-chloro, 4-fluoro (52b) analogs. On the other side a drastic negative effect on potency was revealed on the introduction of larger groups such as 3-bromo-4-methylbenzamido derivative (52c). Furthermore, solubility could be improved by adding heterocyclic group instead of phenyl ring (52d) or an alkyl substituent (52e) but a drop in the potency was observed. SAR of these derivatives 52a-e is explained in Fig. 22.

Fig. 22
figure 22

Chemical structures of 5-aminopyrimidinylquinazolines derivatives (52a–e)

Full size image

In addition, compound 53 (GW2016) (Fig. 23) was discovered to treat cancer cells selectively without affecting normal cells. This compound exerted its effect by inhibiting EGFR and ErbB-2 kinases and inducing apoptosis [101].

Fig. 23
figure 23

Chemical structure of 4-quinazolinamine derivative (GW2016, 53)

Full size image

Furo[2,3-d]pyrimidine derivatives

Miyazaki et al. [102] recorded the synthesis and kinases inhibitory activity of a new series of 5,6-diaryl-furo-4-amino[2,3-d]pyrimidines. This work displayed that methoxyphenylfuro[2,3-d]pyrimidine (54) (Fig. 24) was the most active derivative with IC50 < 3 nM on both VEGFR2 and Tie-2 TK receptors. The activity of this compound was explained based on the X-ray crystal structure, which showed that the urea moiety formed two interactions with amino acids Asp1044 and Glu883. In addition, the amino group and nitrogen atom of the aminopyrimidine form interactions with Glu915 and Cys917.

Fig. 24
figure 24

The chemical structure of new furo[2,3-d]pyrimidine derivative (54) and its binding within VEGFR2

Full size image

In 2008, the same group modified the chemical structure of the previous furo[2,3-d]pyrimidine target compound 54 to change the activity of this compound away from Tie-2/VEGFR2 to target GSK-3 [103]. The structure modifications included the incorporation of the 3-pyridinyl moiety at the 6-position and different sulfonamides and amides at the para position of the 5-phenyl ring. From this series of the modified structure, compound 61 (Fig. 25) exhibited potent GSK-3b inhibitory activity with IC50 = 30 nM. The docking study of compound 61 displayed the aryl ring of the sulfonamide at 5-position appeared to clash with residues Met101, Leu112, and Leu130 of GSK-3. In addition, N3 nitrogen and NH2 of aminopyrimidine are anchored with the carbonyl moiety and NH of Val135, respectively, via hydrogen bond interactions (Fig. 26). Moreover, the 3-pyridine moiety at 6-position is close to Lys85 of the conserved salt bridge (Lys85/Glu97).

Fig. 25
figure 25

Chemical structure of (benzenesulfonylaminophenylpyridyl)furo[2,3-d]pyrimidine 61

Full size image
Fig. 26
figure 26

Binding mode of compound 61 within GSK-3

Full size image

The target furopyrimidine derivative (61) was prepared as illustrated in Scheme 5. Accordingly, sequential acetylation, bromination, and hydroxylation of 4-aminoacetophenone (55) resulted in the α-hydroxyketone (56) which upon treatment with malononitrile in the presence of diethylamine provided 2-amino-3-cyano-furan 57. Reaction of 57 with triethylorthoformate, followed by amination and cyclization in the presence of sodium ethoxide yielded 4-amino-furo[2,3-d]pyrimidine 58. Bromination of 58 at 6-position with NBS followed by Suzuki coupling with 3-pyridineboronic acid pinacol ester gave furopyrimidine 60 which upon removal of the acetyl group and reaction of the resulting amine with benzenesulfonyl chloride provided the target compound (61).

Scheme 5
scheme 5

Synthesis of furo[2,3-d]pyrimidine derivative (61)

Full size image

In addition, a group of 2,4-diaminofuro[2,3-d]pyrimidines were prepared as a novel class of in an attempt to inhibit both dihydrofolate reductase and receptor tyrosine kinases [104]. Compound 62 (Fig. 27) serves as a template for rationally designed VEGFR2 and PDGFR-b inhibitory activity combined with DHFR inhibitory activity in one molecule. Moreover, the candidate compound (63) (Fig. 27) exhibited anticancer and anti-angiogenic activity in mouse HT-29 xenograft model via inhibition of both VEGFR2 and Tie-2 enzymes [105].

Fig. 27
figure 27

Chemical structure of some furo[2,3-d]pyrimidine compounds (62 and 63) with dual inhibitors of receptor tyrosine kinases and dihydrofolate reductase (DHFR)

Full size image

Furthermore, 3-pyridylfuro[2,3-d]pyrimidine derivative 64 (Fig. 28) was synthesized and evaluated for its inhibitory activity against a panel of many kinases [106]. This study demonstrated that compound 64 exhibited selective and potent inhibitory activity against GSK-3b over other tested kinases. Moreover, the furo[2,3-d]pyrimidine derivative 65 (Fig. 28) was found to possess high inhibitory activity against aurora kinase A with IC50 = 159 nM [107].

Fig. 28
figure 28

Chemical structure of some furo[2,3-d]pyrimidine candidates (64 and 65)

Full size image

Conclusion

Pyrimidine ring and its fused derivatives including pyrazolo[3,4-d]pyrimidine, pyrido[2,3-d]pyrimidine, quinazoline, and furo[2,3-d]pyrimidine derivatives have proved as great target molecules in medicinal chemistry and drug development. These scaffolds exerted their effect through inhibiting PKs which are considered as essential enzymes to regulate cell growth, differentiation, migration, and metabolism. This review has highlighted the most promising compounds among these scaffolds based on primary literature. It is anticipated that information given in this review would give rise to design of better molecules with better anticancer activity and increased specificity, and finally will lead to the development of novel synthetic strategies.