Letters in Organic Chemistry - Volume 17, Issue 12, 2020

This review describes the synthesis and reactions of substituted triazolopyrimidines as building blocks toward polyfunctionalized heterocyclic compounds with pharmacological interest.

Enzyme catalyzed synthesis is an eco-friendly technique in organic synthesis, having several benefits over conventional methods. In the present work, we describe a simple process of laccase and chloroperoxidase assisted cyclization of chalcones, leading to the formation of flavanones. The reaction proceeds in a mixture of phosphate buffer and ethanol, under oxygen atmosphere at room temperature, yielding the corresponding flavanone in good to moderate yield. The relative configuration of the products at C2 is tentatively assigned as S*-flavanone based on the coupling constants with the methylenic protons H3α,β. In comparison to the chemical methods, we describe a process which can be achieved efficiently under mild conditions using oxygen as oxidant.

In this work, we proposed the synthesis of a series of pyrazoles derivatives with different substituents on the aromatic rings. We aim to evaluate their influence on the reactivity of the compounds in reactions of α,β-unsaturated chalcones and sulfonyl hydrazide catalyzed by iodine. In order to explain their high and low yields, or the impossibility of obtaining some compounds by applied synthetic methodology, Density Functional Theory (DFT) calculations were performed. The reaction Gibbs free energy (ΔG) as well as the energy gap of the HOMO-LUMO frontier orbitals (ΔE) of some selected reactants could explain qualitatively the experimental observations in terms of synthesis yield. In this way, we believe that the chemical nature of aromatic ring substituents is relevant for the reactivity of the starting materials as well as the formation of the desired products.

Extracts of Carolina jasmine (Gelsemium sempervirens (L.) J.St.-Hil.) petals were evaluated in vitro for inhibition activity against protein tyrosine phosphatase 1B (PTP1B). The principle active agent was also isolated from the extract and identified as ursolic acid (1). This is the first report of ursolic acid from G. sempervirens and of PTP1B-inhibiting activity in the genus Gelsemium.

A straightforward and efficient synthesis of acridine derivatives via a copper-catalyzed cascade reaction among isoxazoles and diaryliodonium salts is achieved. Various mono-, multi-substituted and 9-substituted acridine derivatives could be obtained in moderate to good yields. The process has gone through tandem double arylation and Friedel-Crafts reactions.

A new class of 4H,5H-benzo[4,5]thiazolo[3,2-a]pyrano[2,3-d]pyrimidin-5-one and 5H,6Hpyrano[ 2,3-d]thiazolo[3,2-a]pyrimidin-5-one derivatives were synthesized via the one-pot threecomponent reaction of 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-one and 7-hydroxy-5Hthiazolo[ 3,2-a]pyrimidin-5-one to various aromatic aldehydes and malononitrile. This domino transformation involves the formation of pyranopyrimidine ring by the formation of three C–C bonds and one C– O bond a single synthetic operation. As the products precipitate out of the reaction, simple filtration is enough to gather the products, and thus, there is no need for work-up or column-chromatography. The synthesized thiazole/benzothiazole fused pyranopyrimidine derivatives were evaluated for their antiproliferative activity against four cancer cell lines namely DU 145 (prostate cancer), Hela (Human cervical cancer), MDA-MB-231 (breast cancer), HT-29 (Human colon cancer) and normal cell line HEK293 (human embryonic kidney cells). The results demonstrated that synthesized compounds were selective in its cytotoxicity to cancer cells compared to normal cells. Among these compounds, 2-amino-9- methoxy-5-oxo-4-(3,4,5-trimethoxyphenyl)-4H,5H-benzo[4,5]thiazolo[3,2-a]pyrano[2,3-d]pyrimidine- 3-carbonitrile 4i exhibited the most potent antiproliferative activity against the tested cell lines. Molecular docking studies revealed that these active heterocyclic molecules bind selectively in the colchicine binding site of tubulin polymer.

A series of benzimidazolyl-1,3,4-oxadiazoles (7a-k) were synthesized and evaluated for in vitro anticancer activity against HeLa, MCF7, A549, and HEK293 cell lines. The results indicate that compounds 7b, 7j and 7k have shown excellent anticancer activity and while most of the compounds were non toxic to normal HEK293 cell lines. Molecular docking results of the synthesized compounds with the target Pin1 protein were also discussed.

A series of novel triazole functionalized pyrido [3',2':4,5] furo[3,2-d] pyrimidin-4 (3H)-one derivatives 7a-p were prepared from ethyl furo[2,3-b]pyridine-2-carboxylate 3 on reaction with ammonia to afford furo[2,3-b]pyridine-2-carboxamide 4. This compound, on reaction with triethyl orthoformate TEOF, gave compound 5. Compound 5 on propargylation, followed by a reaction with substituted aryl azides under Sharpless reaction conditions, furnished triazole tagged pyrido [3',2':4,5]furo[3,2-d] pyrimidin-4(3H)-one derivatives. All the products 7a-p were screened against four human cancer cell lines, such as HeLa - Cervical cancer (CCL-2), COLO 205- Colon cancer (CCL-222), HepG2- Liver cancer (HB-8065), and MCF7 - Breast cancer (HTB-22) and one normal cell line (HEK 293). Compounds 7b, 7n, 7o and 7p, which showed promising anticancer activity, were identified and found to be non-toxic to normal cell line. Studies for HeLa, COLO205, HepG2, and MCF-7 using CoMFA and CoMSIA were carried out . Models from 3D-QSAR provided a strong basis for future rational design of more active and selective HeLa, COLO205, HepG2, and MCF-7 cell line inhibitors.