STRUCTURES AND STEREOCHEMICAL ASSIGNMENTS OF SOME NOVEL CHIRAL SYNTHONS DERIVED FROM THE BIOTRANSFORMATION OF 2,3-DIHYDROBENZOFURAN AND BENZOFURAN BY PSEUDOMONAS-PUTIDA

Metabolism of 2,3-dihydrobenzofuran using intact cells of Pseudomonas puyida UV4 gave mainly (3S)-3-hydroxy-2,3-dihydrobenzofuran which was in tum oxidized to an unstable intermediate, (3S,4R,5S)-3,4,5-trihydroxy-2,3,4,5-tetrahydrobenzofuran. Spontaneous dehydration of this cis,cis-triol occurred in the carbocyclic ring to give (3S)-3,5-dihydroxy 2,3-dihydrobenzofuran and in the heterocyclic ring to yield (4R,5S)-cis-4,5-dihydroxy-4,5-dihydrobenzofuran. Bacterial metabolism of benzofuran was found to occur in the carbocyclic ring to form (6S,7S)-cis-6,7-dihydroxy-6,7-dihydrobenzofuran and its dehydration product, 6-hydroxybenzofuran. Dioxygenase-catalysed cis-dihydrodiol formation in the heterocyclic ring of benzofuran (to give cis-2,3-dihydroxy-2,3-dihydrobenzofuran as a transient intermediate) is proposed to account for the appearance of (1R)-1,2-dihydroxy-1-(2'-hydroxyphenyl)ethane as a major metabolite of benzofuran. cis-4,5-Dihydroxy-4,5-dihydrobenzofuran and cis-6,7-dihydroxy-6,7-dihydrobenzofuran are potentially valuable chiral synthons which can be added to the small pool of bicyclic cis-dihydrodiol metabolites currently available for synthesis.