First synthesis of asperopterin A, an isoxanthopterin glycoside from Aspergillus oryzae

The key precursor, N 2-(N,N-dimethylaminomethylene)-6-hydroxymethyl-8-methyl-3-[2-(4-nitrophenyl)ethyl]-7-xanthopterin (16) was efficiently prepared from 2,5-diamino-6-methylamino-3H-pyrimidin-4-one (5) and ethyl 3-(tert-butyldimethylsilyloxy)-2-oxopropionate (12), followed by the protection of the pteridine ring. Glycosylation of 16 with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose (18) in the presence of tin(IV) chloride yielded the corresponding β-D-ribofuranoside. Successive removal of the protecting groups of the resulting D-ribofuranoside provided asperopterin A (4b).