María Soledad Pino-González

Asymmetric synthesis of 2,3-epoxyamides by reacting monosaccharide derivatives with stabilised sulphur ylides generated in-situ: two-phase method and configurational assignations

Abstract The reaction of 2,3- O -isopropylidene-D-glyceraldehyde 1 ,2,4-ethylidene-D-threose 7 , or 2,3:4,5-di- O -isopropylidene-D-arabinose 9 with N,N-dimethyl-carbamoylmethyldimethylsulphonium chloride and a 10–50% solution of sodium hydroxyde gave the corresponding 2,3-epoxyamides 5, 8 and 10 , and the reaction of 1 , or 5- O -trityl-2,3- O -isopropylidene-D-ribofuranose 13 with N,N-diethylcarbamoylmethyl dimethyl sulphonium chloride and a 10–50% solution of sodium hydroxyde gave the corresponding 2,3-epoxyamides 4 and 14 , respectively, with high yields and variable stereoselectivity.

A New Synthesis of 2-C-Methyl-d-Ribono-1,4-Lactone and the C-9/C-13 Fragment of Methynolide

Abstract The synthesis of the glucosaccharino lactone, 2-C-methyl-D-ribono-1,4-lactone 7 from 2,3-O-isopropylidene-D-glyceraldehyde 1 is reported. Lactone 7 was transformed into (2R,3R)-2,3-dihydroxy-2-methylpentanoic acid 18 (the C-9/C-13 fragment of Methynolid) by two new procedures which improve on existing alternatives: conversion of the epoxide derivative 9 to the episulfide 14 and subsequent reduction; and reductive opening of the 5-bromo derivative of 2,3-O-isopropylidene-2-C-methyl-D-ribono-1,4-lactone and subsequent hydrogenation.

Stereoselective synthesis of 2,3-epoxy-amides by aldol-like condensation of 2,3-O-isopropylidene-D-glyceraldehyde with N,N-diethyl diazoacetamide

Abstract The 1:1 mixture of cis:trans epoxy-amides 5c was obtained quantitatively by condensation of 2,3-O-isopropylidene-D-glyceraldehyde 1 with N,N-diethyl diazoacetamide. Similarly, the reaction of 1 with methyl diazopropionate was studied and gave as the main product the β-ketoester 4b (product of a 1,2-hydrogen shift) and, in a low yield, the glycidic ester 5b (intramolecular nitrogen displacement). The configuration at C-3 of the resultant epoxides of both reactions revealed that the addition step was completely stereoselective. Under similar conditions, compound 6 , methyl 3-hydroxy-2-diazopropionate was unreactive, but with heating gave 7 .

Stereoselective synthesis of precursors of the macrolide antibiotics via reactions of sulfur ylides with chiral aldehydes

Abstract Reactions of stabilized sulfur ylides with chiral aldehydes provided epoxides with high stereoselectivity. The opening of the resulting epoxides with lithium dimethyl cuprate gave 2-methyl-3-hydroxy amides which represent potentially useful building blocks for the synthesis of macrolide natural products. These amides were transformed into chiral aldehydes, with a methyl group in the α-position, and were reacted, in a iterative process, with a sulfur ylide reagent to give, in high yield and stereoselectivity, the epoxides with the stereochemistry according to Felkin-Ahn control. Finally, opening of the epoxide with the Gilman reagent provided a compound with four stereocenters occurring in the macrolide-type of natural products.

Palytoxin-related C-Glycosides: a Conformational Study using Molecular Mechanics and an Analysis of Coupling Constants

Abstract The conformational behaviour of ten D-gluco- or 2-deoxy-D-gluco-C-glycosides related to Palytoxin were studied. Theoretical coupling constants were deived by applying altonas empirical generalization of Karplus equation to the torsional angles and conformational populations. The global rms (root-mean-square) deviation of the calculated coupling constants from experimental values was 0.873 Hz.