F13459, a new derivative of mycophenolic acid. II. Physico-chemical properties and structural elucidation.

F13459 is a new inhibitor of synthesis and trafficking of virus glycoprotein isolated from the culture broth of a Penicillium sp. The molecular formula of F13459 was determined to be C27H28O11 by HRFAB-MS and NMR spectral analyses. The structure of F13459 was elucidated to be 3,4-dihydro-3,4,6,8-tetrahydroxy-3-methyl-1H-2-benzopyran-1-one 4-O-mycophenolate, an ester derivative of mycophenolic acid. F13459 was isolated as the optically inactive form. F13459 exists in epimeric mixtures at C-3' through relatively fast hemiacetal-ketone tautomerism and at C-4' through slow keto-enol tautomerism. Those epimerizations were confirmed by NOE differential experiments for fast chemical exchange and equilibrium and by deuteration experiments in NMR for slow chemical exchange.