An Improved Synthesis of a Key Intermediate for Glycosylation of Biopterin and Its Application for the First Synthesis of Microcystbiopterin B

ABSTRACT A key intermediate for the selective 2′‐ O ‐glycosylation of biopterin, N 2 ‐( N,N ‐dimethylaminomethylene)‐1′‐ O ‐(4‐methoxybenzyl)‐3‐[2‐(4‐nitrophenyl)ethyl]biopterin ( 12 ), was efficiently synthesized via a novel route starting from d ‐glucose, leading to an improved overall yield. This new pathway involves the preparation of a 5‐deoxy‐ l ‐arabinose phenylhydrazone derivative ( 9 ) as a crucial intermediate in the construction of the pteridine ring. Utilizing compound 12 , the first synthesis of microcystbiopterin B ( 4 ) was accomplished by glycosylation of 12 with 4,6‐di‐ O ‐acetyl‐2‐ O ‐(4‐methoxybenzyl)‐3‐ O ‐methyl‐α‐ d ‐glucopyranosyl bromide ( 19 ) in the presence of silver triflate and tetramethylurea, followed by stepwise deprotection.