Efficient total syntheses of natural neopterin glycosides: Neopterin glucronide and solfapterin

1,2-Di-O-acetyl-N²-(N,N-dimethylaminomethylene)-3-[2-(4-nitrophenyl) ethyl]neopterin (11a) and its 1,2-di-O-benzoyl analog (11b) were prepared from neopterin in 5 steps, respectively. Glycosylation of 11a with methyl 2,3,4-tri-O-benzoylD-glucopyranosyluronate bromide (15b) in the presence of silver triflate afforded the corresponding 3'-O-(β-D-glucopyranosyl) neopterin derivative (18) in 64% yield. The similar treatment of 11b with 2-azido-3,4,6-tri-O-benzoyl-2-deoxy-a-D-glucopyranosyl bromide (21b) provided the corresponding 3'-O-(α-D-glucopyranosyl)neopterin derivative (23a) in 58% yield. The first syntheses of neopterin glucronide (5) and solfapterin (6) were achieved by successive removal of the protecting groups of 18 and 23a, respectively.