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.