Novel Preparation of a 2′-O-Acetyl-1′-O-(4-methoxybenzyl)-l-biopterin Derivative, a Versatile Precursor for a Selective Synthesis of l-Biopterin Glycosides

l-Rhamnose was converted, over a 13-step-sequence, into 2′-O-acetyl-N 2-(N,N-dimethylaminomethylene)-1′-O-(4-methoxybenzyl)-3-[2-(4-nitrophenyl)ethyl]-l-biopterin, an appropriately protected precursor of 1′-O- and 2′-O-monoglycosyl-l-biopterin. Thus, the first selective synthesis of these l-biopteri