Anup Bhattacharjya

Synthesis of chiral oxepanes and pyrans by 3-O-allylcarbohydrate nitrone cycloaddition (3-OACNC)

3-O-Allylcarbohydrate nitrone cycloaddition (3-OACNC) furnished pyran and oxepane derivatives from 3-O-allyl hexose N-benzyl nitrones and 3-O-allyl furanoside-5-aldehyde N-benzyl/methyl nitrones. The regioselectivity of 3-OACNC was found to depend on the following factors (a) the structural nature of the nitrone (b) substitution and stereochemistry at 3-C of the carbohydrate backbone (c) substitution at the terminus of the O-allyl moiety. Oxepanes or pyrans obtained from a particular set of a hexose nitrone and the corresponding furanoside nitrone were converted to enantiomeric cyclic ethers through degradation. A mixture of an oxepane and a pyran was formed in the intramolecular oxime olefin cycloaddition (IOOC) of a 3-O-allylcarbohydrate derived oxime.

An expeditious enantiodivergent synthesis of chiral oxepanes from D-glucose by the application of intramolecular 1,3-dipolar nitrone cycloaddition

Abstract The enantiomers of an oxepanoisoxazolidine and a chiral oxepane, potentially useful as precursors for naturally occurring oxepanes, were synthesised from D-glucose involving intramolecular 1,3-dipolar nitrone cycloaddition.

Synthesis of chiral pyranocyclohexane, oxepanocyclohexane, and furylpyran and -oxepane systems by the application of intramolecular nitrone and nitrile oxide cycloaddition of carbohydrate derivatives

Abstract Chiral nonracemic pyranocyclohexanes 7 and 8 and oxepanocyclohexane 11 and 12 were obtained from a single 1,2-isopropylidene-3-O-cyclohexenyl carbohydrate aldehyde 4 via intramolecular nitrile oxide cycloaddition, and were converted to 2-(2′-tetrahydrofuryl)pyran 28, which incorporates the lasalocid skeleton, and the related oxepane derivative 32 respectively, through modification of the furanoside ring by applying 2-O-allyl carbohydrate nitrone cycloaddition.

Bharatamine - a unique protoberberine alkaloid from alungium lamarckii thw., biogenetically derived from monoterpenoid precursor

Abstract Bharatamine (I), mp 182–183°, a novel racemic protoberberine alkaloid unoxygenated at ring D and biogenetically derivable from loganin, a pathway hitherto unknown for this class of compounds, has been isolated from the seeds of Alanguim lamarckii and structure established by an unequivocal synthesis.

Synthesis of optically pure tetrahydrofurans from 2-o-allylglucose derivatives by intramolecular nitrone cycloaddition: preferential formation of a furanoisoxazolidine from penta-o-allylglucose

Abstract Intramolecular nitrone cycloaddition of 2- O -allyl-3,5,6-tri- O -benzylglucose and penta- O -allylglucose afforded optically pure trisubstituted tetrahydrofurans.

Synthesis of chiral oxepinopyran and oxepinooxepane systems from 1,2-isopropylidene furanoside ring-fused cyclic ether derivatives through 4-O-allyl nitrone and nitrile oxide cycloadditions

Abstract A novel strategy was developed by which chiral oxepinopyran and oxepinooxepane derivatives were synthesised from 1,2-isopropylidene furanoside fused pyran and oxepane derivatives by the cycloaddition of 4- O -allyl nitrone or nitrile oxide species generated from the furanoside ring

Expeditious synthesis of chiral six and seven membered nitrogen heterocycles from carbohydrate amines by N-allyl carbohydrate nitrone cycloaddition: Tuning of regioselectivity by N-substitution

Abstract The cycloaddition of N -allyl carbohydrate nitrones leads to enantiomerically pure six and seven membered nitrogen heterocycles and the regioselectivity of the cycloaddition can be tuned by changing the substituent on the nitrogen atom.

Regioselective synthesis of chiral six- and seven-membered N-heterocycles from N-allyl carbohydrate nitrones: Tuning of regioselectivity by N-substitution

Abstract The intramolecular cycloaddition of N-allyl carbohydrate nitrones leads to enantiomerically pure six- and seven-membered nitrogen heterocycles and the regioselectivity of the cycloaddition was controlled by changing the substituent on the nitrogen atom of the N-allyl moiety.

Studies on indian medicinal plants : part 91 1 -structure and synthesis of alamaridine, a novel 5-methylbenzopyrioquinolizine alkaloid from alangium lamarckii

Abstract The structure of alamaridine (1) a novel benzopyridoquinolizine alkaloid, was established by spectral data. However, its stereochemistry could only be determined now by a total synthesis involving the key cyclisation of an 1-methyl-2-pyridylmethyl-3,4-dihydroisoquinolinium salt 19a in presence of pivaloyl chloride and triethylamine. O-Benzyldehydroalamaridine thus formed was reduced by sodium cyanoborohydride and then deprotected to obtain alamaridine (1) and 5-epi-alamaridine (26). Isoalamaridine (27) and its 5-epimer (28) were also synthesised following the same route.

Structure and synthesis of alamaridine, a novel benzopyridoquinolizine alkaloid from alangium lamarck II

Abstract Synthesis of ( + )-alamaridine ( 1 ) from the N -pyridylmethyl dihydroisoquinolinium salt 3 via pivaloyl chloride induced cyclisation to 4 and subsequent reduction with sodium cyanoborohydride in acetic acid established the structure and relative stereochemistry at the chiral centres of this unique 5-methylbenzopyridoquinolizine alkaloid isolated from A. lamarckii Thw.