nan Poonam

Naturally occurring aristolactams, aristolochic acids and dioxoaporphines and their biological activities

Aristolactams, having a phenanthrene chromophore are a small group of compounds mainly found in the Aristolochiaceae together with the aristolochic acids and 4,5-dioxoaporphines. In this report, these three important classes of natural products are reviewed and classified on the basis of their oxygenation pattern. In addition the biological activities of these compounds and their general chemistry are discussed.

Potential use of a novel lipase from Aspergillus carneus in deacetylation reactions

A novel lipase from Aspergillus carneus has been used in organic solvents for efficient regioselective and chemoselective deacetylation of the peracetates of polyphenolic aromatic ketones, esters and amides. A reversal of regioselectivity was observed as compared with the results obtained during deacetylation with porcine pancreatic lipase (PPL).

Utility of a novel lipase from Aspergillus terreus in deacetylation reactions

A novel lipase from Aspergillus terreus has been used in organic solvents for regioselective deacetylation of the peracetates of polyphenolic aromatic ketones. A reversal of regioselec-tivity to that obtained during deacetylation with porcine pancreatic lipase (PPL) has been observed.

Synthesis and lipase-mediated stereoselective deacetylation of (±)-3-acetoxymethyl-3-alkyl-7-methoxychroman-4-ones

Abstract Six (±)-3-acetoxymethyl-3-alkyl-7-methoxychroman-4-ones have been synthesized in four steps starting with the coupling of resorcinol with corresponding aliphatic acid leading to the formation of 2,4-dihydroxyphenyl alkyl ketones, which upon monomethylation and hydroxymethylation, followed by acetylation afforded the racemic acetoxymethylated compounds in 17–30% overall yields. Candida rugosa lipase-catalyzed deacetylation of (±)-3-acetoxymethylchromanones in diisopropyl ether exhibited fairly moderate enantioselectivity.

Lipase-catalysed regio- and enantioselective deacetylation of 2,4-diacetoxyphenyl alkyl ketones.

Porcine pancreatic lipase in tetrahydrofuran catalyses the deacetylation of 2,4-diacetoxyphenyl alkyl ketones in a highly regioselective fashion. The strategy of regioselective deacetylation of diacetoxyphenyl alkyl ketones has also resulted in the enantiomeric resolution of a racemic diacetoxyphenyl alkyl ketone, i.e. (+/-)-2,4-diacetoxyphenyl (1-ethyl)pentyl ketone, a precursor for the synthesis of an antifungal coumarin, 7-acetoxy-4-(1-ethyl)pentyl-3-phenyl-2H-1-benzopyran-2-one.

Selective transacylation reactions on 4-aryl-3,4-dihydropyrimidin-2-ones and nucleosides mediated by novel lipases*

Different (±)-4-(3/4-acetoxyaryl)-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-ones have been synthesized and subjected to enantioselective deacetylation reactions mediated by different lipases in organic media. Novozyme 435 in tetrahydrofuran:diisopropyl ether was found to be the catalyst of choice for efficient enantioselective deacetylation of dihydropyrimidinones under study. Further, we discovered that lipase isolated from Pseudomonas aeruginosa can be used for selective acylation of secondary hydroxyl groups in nucleosides. This observation can be very useful for selective manipulation of different hydroxyl groups in nucleosides.