Abstract: Eupenicillum sp. E-UN41 was obtained in the course of screening for bioactive microbial products, the compound UN41A was isolated by column chromatography of ion exchange resin and Sephadex G10, and purified by crystallization. The configuration and stereochemistry structure of UN41A were determined by NMR spectra and single crystal X-ray diffraction. UN41A was proved to be 4-carbamoyl-1-B-D-ribofuranosyl imidazolium-5-olate, the same structure as the immunosuppressant, mizoribine. The crystal of UN41A belonged to the orthorhombic P212121 space group with a = 7. 4897(7), b = 11.3801 (15), c = 14.0090 (13) ?, V = 1194.0(2) ?3, Z=4, Dc=1.553g/m3, F (000) =592. The crystal of UN41A revealed that there was a imidazole ring plane.

Key words: Eupenicillum, isolation and purification, crystal structure, Mizoribine