Pterins. IX. The conformations of (6R)- and (6S)-2-Amino-6-[(1'R,2'S)-1',2'- dihydroxypropyl]-5,6,7,8-tetrahydropteridin-4(3H)-one [L-erythro-5,6,7,8-Tetrahydrobiopterin] hydrochlorides and their tetraacetyl derivatives

Abstract

Catalytic reduction of biopterin (1) in trifluoroacetic acid gives, after acetylation, a 1 : 3 mixture of (6S)- and (6R)- (4) tetraacetyl-5,6,7,8-tetrahydrobiopterin. Catalytic reduction of triacetylbiopterin (2) in ethanol yields, after acetylation, a 3 : 1 mixture of (6S)- and (6R)- (4) tetraacetyl- 5,6,7,8-tetrahydrobiopterins. These were separated and gave on hydrolysis (6S)- and (6R)-(3) 5,6,7,8- tetrahydrobiopterin hydrochloride. The diastereomeric acetyl derivatives and hydrochlorides have distinct 1H n.m.r. spectra which can be used to identify them, and provide information about the conformations of the tetrahydropyrazine rings and the 6-dihydroxypropyl side chains.