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-N²-(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-biopterin glycosides was accomplished by treatment of the precursor with either DDQ or sodium methoxide, then with tetra-O-benzoyl-α-D-glucopyranosyl bromide in the presence of silver triflate and tetramethylurea, followed by removal of the remaining protecting groups.