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-beta-D-ribofuranose (18) in the presence of tin(IV) chloride yielded the corresponding beta-D-ribofuranoside. Successive removal of the protecting groups of the resulting D-ribofuranoside provided asperopterin A (4b).

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