Pranjal P. Bora

Beyond enzymatic promiscuity: asymmetric induction by L-proline on lipase catalyzed synthesis of polyfunctionalized 4H-pyrans

We report herein the synthesis of polysubstituted 4H-pyrans catalysed by PPL via a three-component reaction of aldehyde, malononitrile and acetyl acetone. The catalytic activity of PPL with other lipases and its reactivity profile in different reaction media were thoroughly studied. Although the change in enzyme reaction specificity induced by metal substitutions and amino acids is well known, non-covalent introduction of an amino acid into an enzymatic promiscuous reaction to achieve stereoselectivity through co-operative catalysis has not been explored yet. In an interesting observation, we have noted that addition of L-proline to PPL catalysed reactions can induce stereoselectivity in the formation of polysubstituted 4H-pyrans while such MCRs catalyzed by PPL alone give only racemic products.

PPL catalyzed four-component PASE synthesis of 5-monosubstituted barbiturates: Structure and pharmacological properties.

Enzymatic four-component reactions are very rare although three-component enzymatic promiscuous reactions are widely reported. Herein, we report an efficient PASE protocol for the synthesis of potentially lipophilic zwitterionic 5-monosubstituted barbiturates by four component reaction of mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde and barbituric acid in ethanol at room temperature. Seven different lipases were screened for their promiscuous activity towards the synthesis of 5-monosubstituted barbiturates and the lipase from porcine pancreas (PPL) found to give optimum efficiency. The zwitterionic 5-monosubstituted barbiturates with pyrazolyl ring showed promising pharmacological activity upon screening for antibacterial and apoptotic properties.

A Practical Catalyst-Free Synthesis of 6-Amino-4 Alkyl/Aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-carbonitrile in Aqueous Medium

A completely green and improved method for the synthesis of 6-amino-4-aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-carbonitriles by a four-component reaction of a mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde, and malononitrile in boiling water is reported. Similar synthesis starting from aliphatic aldehydes was carried out in water: ethanol (1 : 1) at reflux temperature without using any catalyst.

NEW METHOD FOR THE SYNTHESIS OF ETHER DERIVATIVES OF ARTEMISININ

Abstract Dihydroartemisinin can be converted to its ether derivatives in good yields by reaction with different alcohols in the presence of a catalytic amount of dodecatungstophosphoric acid hydrate. Easy handling, trouble-free workup by filtration, excellent yields, and very short reaction times are some of the highlights of this protocol. GRAPHICAL ABSTRACT

A green four-component synthesis of zwitterionic alkyl/benzyl pyrazolyl barbiturates and their photophysical studies.

A novel series of unsymmetrically substituted alkyl/benzyl pyrazolyl barbiturates incorporating highly biologically active pyrazolone and barbiturate moieties was synthesized by four-component reactions of a mixture of ethyl acetoacetate, hydrazine hydrate, aldehydes and barbituric acid/thiobarbituric acid in ethanol without using a catalyst. The photophysical properties of the newly designed alkyl/benzyl pyrazolyl barbiturates were studied, and good quantum yield of some products indicated a definitive scope in the field of biochemical applications. Single-crystal X-ray crystallographic studies revealed that the newly synthesized compounds exist in zwitterionic form. The zwitterionic nature of the new chimera makes them interesting candidates for drug delivery as zwitterionic drugs are known to have highly water soluble properties, specific protein absorption, slow recognition by immune system, slow blood clearance from body and can constantly diffuse and deposit throughout the physiological pH.

Synthesis of Polyfunctionalized 4H-Pyrans

Amberlyst A21 catalyzed one-pot three-component coupling of aldehyde and malononitrile with active methylene compounds such as acetylacetone and ethyl acetoacetate for the synthesis of pharmaceutically important polyfunctionalized 4H-pyrans has been reported. Simple experimental procedure, no chromatographic purification, no hazardous organic solvents, easy recovery and reusability of the catalyst, and room temperature reaction conditions are some of the highlights of this protocol for the synthesis of pharmaceutically relevant focused libraries.