Anubha Sharma

Metal‐Dependent Reaction Tuning with Cyclopentylmetal Reagents: Application to the Asymmetric Synthesis of (+)‐α‐Conhydrine and (S)‐2‐Cyclopentyl‐2‐phenylglycolic Acid

The reaction profile of the cyclopentyl organometallic reagents with the aliphatic ketones can be tuned to reduction or addition by changing the metal atom. Cyclopentylmagnesium bromide (CPMB) reduces aromatic and aliphatic aldehydes and ketones to the corresponding alcohols without any C-C bond formation and shows good diastereoselectivity in the reduction of the substituted cyclic and polycyclic ketones as well as chiral alpha-oxygenated aliphatic ketones. However, in the presence of 10 mol % of ZnCl(2), the cyclopentylmagnesium halides follow a normal Grignard addition to the ketones to give tertiary alcohols with complete diastereoselectivity. The reductive as well as the addition protocols were used for the asymmetric synthesis of two medicinally important compounds, (+)-alpha-conhydrine and (S)-2-cyclopentyl-2-phenylglycolic acid.

A chemoenzymatic synthesis of hept-6-ene-2,5-diol stereomers: application to asymmetric synthesis of decarestrictine L, pyrenophorol, and stagonolide E.

The stereomers of hept-6-ene-2,5-diol derivatives were conceived as useful chiral intermediates and were synthesized starting from sulcatol using two lipase-catalyzed acylation reactions as the key steps. The versatility of the intermediates was demonstrated by converting them to the titled tetrahydropyran, macrolide, and macrodiolide compounds using standard synthetic protocols.

Synthesis of the 1,5-dimethylic chiron enantiomers, 3,7,11-trimethyldodec-10-en-1-ol: application to enantiomeric syntheses of tribolure and a marine fatty acid

Abstract A convenient synthesis of the title chiron antipodes has been developed starting from (±)-citronellol via a sequential acetylation protocol using two lipases. The different stereoisomers of the chiron were then functionalized by simple routes to (4R,8R)-dimethyldecanal, an insect pheromone and (5R,9R)-5,9,13-trimethyltetradecanoic acid, a marine phospholipid fatty acid.

Convenient synthesis of (±)- and (S)-antipode of (4E,7S)-7-methoxytetradec-4-enoic acid, the antimicrobial principle of marine cyanophyte

Abstract The (±)- and ( S )-isomers of title compound I were prepared via a short and efficient route. The key features of the synthesis were the use of easily accessible materials, operationally simple reaction protocol and highly enantioselective lipase catalyzed esterification for the generation of the required chiron.

CHEMOENZYMATIC SYNTHESIS OF (S)-EICOS-(4E)-EN-1-YN-3-OL, THE CYTOTOXIC PRINCIPLE OF THE MARINE SPONGE, CRIBROCHALINA VASCULUM

Abstract An efficient enantioselective synthesis of the title compound I was developed from the versatile chiron 1- tert -butyldimethylsilylpenta-1,4-diyn-3-ol 2 . The chiron, in turn, was prepared via a combination of lipase catalyzed acylation–alcoholysis protocol. Protection of its hydroxy group, alkylation with a suitable bromide and subsequent functionalization gave ( S )- I with high enantiomeric purity.

[bmim][Br] as a Solvent and Activator for the Ga-Mediated Barbier Allylation: Direct Formation of an N-Heterocyclic Carbene from Ga Metal

The room-temperature ionic liquid (RTIL) [bmim][Br] has been found to be an excellent green and inexpensive medium for the Ga-mediated allylation of aromatic and aliphatic aldehydes and ketones. The RTIL activated the metal via formation of a Ga-N-heterocyclic carbene complex that assisted in the completion of the reaction at ambient temperature with only 0.5 equiv of Ga and 1.2 equiv of allyl bromide with respect to the carbonyl substrates. The present protocol required a much shorter time than those reported in the literature using other metals and solvents and proceeded with good yields and excellent selectivity.

Enantio-reversal in Candida rugosa lipase-catalyzed esterification of 3-hydroxybutyric acid

Abstract Candida rugosa lipase (CRL)-catalyzed esterification of racemic 3-hydroxybutyric acid with different nucleophilic alcohols was studied. The alcohol chain length was found to have a profound role in the enantioselectivity of the reaction. As compared to the esterification with 1-butanol, use of longer alcohols surprisingly led to an enantio-reversal. Under optimized condition, the ( R )-ester with 95–98% enantiomeric excess (ee) was obtained when the esterification was carried out with 1-hexanol and 1-octanol in the presence of freshly activated molecular sieve 4 A.

ENANTIOSPECIFIC SYNTHESIS OF SOME BIOACTIVE AMINO ALCOHOLS AND RELATED COMPOUNDS FROM CYCLOHEXYLIDENEGLYCERALDEHYDE

Abstract Two bioactive amino alcohols or related derivatives, 2-aminohexadecanol I and erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA hydrochloride) IIa, have been synthesized from some enantiomerically pure 3-alkylglycerols. The required C-3 epimeric 3-alkylglycerols were, in turn, prepared by simple Grignard addition to cyclohexylideneglyceraldehyde 1 followed by column chromatography.

Studies on PPL Catalyzed Acetylation of 2-Alkanols: Its Application for the Synthesis of 2-Dodecanol and 2-Tridecyl Acetate, the Pheromones of Crematogaster Ants and Drosophila mulleri Flies

Abstract Several aliphatic 2-alkanols with varying chain length has been efficiently resolved by their acetylation using vinyl acetate/PPL in diisopropyl ether. The effect of solvent polarity, position and type of unsaturation and chain length has been probed. This has led to more convenient synthesis of some insect pheromones.

PPL catalyzed monoesterification of α,ω-dicarboxylic acids

SummaryA regioselective strategy for PPL catalysed monoesterification of aliphatic α,ω-dicarboxylic acids with n-butanol have been developed. In addition to high regioselectivity, the method also ensures chemoselective esterification of a saturated acid moiety in presence of a conjugated acid function.