Ch. Prasad Rao

Claisen Rearrangement of 4-Propargloxycoumarins: Formation of 2H,5H-Pyrano[3,2-c][1]benzopyran-5-ones

Abstract The Claisen rearrangement of 4-propargyloxycoumarins affords 2H, 5H-pyrano[3,2-c][1]benzopyrans-5-ones as the only product. The effect of solvent on the Claisen rearrangement has been examined.

A New and Facile Synthesis of Chroman-3-ols, 3,4-Dihydro-2H-[1]-Benzopyran-3-ols

Abstract o-Allyl phenols react with m-chloroperoxybenzoic acid (m-CPBA) in dry chloroform to give chroman-3-ols in a single step in good yields (93–96%).

Synthesis and antimicrobial assessment of novel coumarins featuring 1,2,4-oxadiazole

Abstract Oxadiazoles are heterocyclic compounds with a variety of application in many pharmaceuticals and agrochemical products. We report herein the convenient synthesis of 4-[(3-aryl-1,2,4-oxadiazol-5-yl)methoxy]-coumarins (4a–f), 6-[(3-aryl-1,2,4-oxadiazol-5-yl)methoxy]-4-methylcoumarins (7a–f) and 7-[(3-aryl-1,2,4-oxadiazol-5-yl)methoxy]-4-phenylcoumarins (10a–f) in high yields by one-pot condensation reaction of esters with amidoximes. The structures of the synthesized compounds were established on the basis of IR, NMR and mass spectrometry. The antibacterial and antifungal activities of synthesized compounds were evaluated. Graphical Abstract

Synthesis of novel forskolin isoxazole derivatives with potent anti-cancer activity against breast cancer cell lines

Forskolin C1-isoxazole derivatives (3,5-regioisomers) (11a-e, 14, 15a-h and 15, 16a-g) were synthesized regioselectively by adopting 1,3-dipolar cycloadditions. These derivatives were tested using estrogen receptor positive breast cancer cell lines MCF-7 and BT-474. Majority of the compounds exhibited activity against the p53-positive MCF-7 breast cancer cells but not against the p53-negative BT-474 breast cancer cells. Among forskolin derivatives, compounds 11a, 11c, 14a, 14f, 14g, 14h, 15b, 16g and 17b exhibited higher anti-cancer activity against MCF-7 cell line with an IC50≤1µM. The derivative 14f exhibited highest activity in both p53-positive (MCF-7) and p53-negative (BT-474) breast cancer cell lines with an IC50 of 0.5µM.

Synthesis of novel substituted pyrano annulated flavones

A simple and efficient one pot method has been developed for the synthesis of some new functionalized pyrano fused flavone derivatives, alkyl 4,8-dioxo-2-phenyl-4,8-dihydropyrano[2,3-f]chromene-10-carboxylates and dialkyl 4-oxo-2-phenyl-4,8-dihydropyrano[2,3-f]chromene-8,9-dicarboxylates, from 7-hydroxy flavones and 7-hydroxy 8-formyl flavones using dialkylacetalynedicarboxylates in the presence of triphenyl phosphine. The structures of all synthesized compounds were elucidated by FT-IR, 1H and 13C NMR and Mass spectral analysis.

Synthesis of pyrazole-substituted chromene analogues with selective anti-leukemic activity

We report design and synthesis of a series of flavanone/chromene derivatives containing pyrazoles 6a–6h and 8a–8e with potent anti-leukemic activity. Anti-leukemic activity of novel flavanone derivatives was tested using the K562 cell line. The parental flavanone was selected as the reference compound in identification of analogues with superior anti-leukemic activity. More than two-thirds of the derivatives displayed higher activity than the initial flavanone. Positions of substituents that promoted anti-leukemic activity were identified on both the chromene and pyrazole fragments. Compounds 6b and 6c showed the highest activity against K562 cell line, with IC50 values 3.0 and 0.5 μM respectively. Notably, compounds 6b and 6c displayed very high selectivity in inhibition of leukemic cells (K562) but not of healthy HEK293 cells or solid cancer cell lines HeLa, MCF7 and BT474. Moreover, both the 6b and 6c compounds were predicted to have good ADME properties.

Synthesis and antimicrobial evaluation of novel urea derivatives from chromene based oxadiazole amines

A series of novel aryl ureides were synthesized based on oxadiazoles and different substituted aromatic amines. The intermediate amine, (3-(2H-chromen-3-yl)-1,2,4-oxadiazol-5-yl)methanamines (6a) was reacted with aromatic amines in presence of triphosgene to obtain the urea derivatives 7a–d and 7e–i in high yields. The structures of all the intermediates and the final urea derivatives were established by IR, NMR and mass spectrometry data. The antibacterial activity of synthesized compounds was evaluated against two gram-negative bacteria namely Escherichia coli and Pseudomonas aeroginosa and it was observed that the urea derivatives 7a and 7i were promising antibacterial agents.