Synthesis of DL-6'-Epivalidoxylamine A

Abstract

Validamycin A [1] is a main component of antibiotic validamycin complex, which is produced by Streptomyces hygroscopicus var. limoneus and is used to control sheath blight in rice plants. The structure of [ 1 ] is assigned as the β-D-glucopyranoside of validoxylamine A 2], which is composed of two branched-chain cyclitols bonded by way of an imino linkage. [In order to elucidate the structure-activity relationship of this kind of antibiotics, a racemic isomer of [2] was synthesized. Reaction of the DL-epoxycyclohexene [ 8], a precursor of unsaturated branched-chain cyclitol portion, with a blocked DL-validamine [16] yielded the blocked 6'-epimer [3 a, b] of [2 ]. Separation of racemic diastereomers of [3] was achieved by converting it into the corresponding octaacetates [20 a, b], followed by fractionation by column chromatography on silica gel. Synthetic Studies on the Validamycins. VI.