Doubly carbon-branched pentoses: synthesis of both enantiomers of 2,4-di-C-methyl arabinose and 2-deoxy-2,4-di-C-methyl arabinose using only acetonide protection

A common and versatile synthetic route to (-) and (+) pentenomycin I, (+) halopentenomycin I and dehydropentenomycin

A versatile and stereoselective total synthesis of (+) and (-) pentenomycin I, (+) halopentenomycins I and dehydropentenomycin from a common chiral polyhydroxylated cyclopentene through oxidation and protection/deprotection has been described. Stereoselective hydroxymethylation, stereoselective Grignard reaction and ring closing metathesis are the key features of our approach.

6-De-oxy-3,4-O-isopropyl-idene-2-C-methyl-l-galactono-1,5-lactone

X-ray crystallography unequivocally confirmed the stereochemistry of the 2-C-methyl group in the title mol­ecule, C₁₀H₁₆O₅, in which the 1,5-lactone ring exists in a boat conformation. The absolute stereochemistry was determined by the use of d-ribose in the synthesis. The crystal exists as O—H⋯O hydrogen bonded chains of mol­ecules running parallel to the a axis with each mol­ecule acting as a donor and acceptor for one hydrogen bond.

3,4-O-Isopropyl-idene-2-C-methyl-d-galactonolactone

X-ray crystallography unequivocally confirmed the stereochemistry of the 2-C-methyl group in the title mol­ecule, C₁₀H₁₆O₆, in which the 1,5-lactone ring exists in a boat conformation. The use of d-galactose in the synthesis determined the absolute stereochemistry. The crystal exists as O—H⋯O hydrogen-bonded layers in the ab plane, with each mol­ecule acting as a donor and acceptor for two hydrogen bonds.