The X-ray crystal reflection was carried out to determine the structure of elsinochrome A (EA), obtained by biological fermentation in laboratory as a purple-red single crystal C~3~0H~2~4O~1~0 : M~r=544.49, orthorhombic, a=1.2421(2) nm, b=1.3037(2) nm, c=1.4927(3) nm, V=2.4172(7)nm^3, D~c=1.496 g·cm^3, Z=4, F(000)=1136, μ=0.113nm^- ^1, R=0.0347(3726 observed reflections), P2~12~12~1. Compared with the results published, an obvious configuration difference exists in the side-groups of perylenequinone ring and the two chiral carbon atoms are R-R types especially. Ab initio calculations of the EA have been investigated at STO-3G level by two different beginning structures which are from X-ray analysis and molecular mechanics optimization respectively. The calculation results show that the EA is a new optical stereoisomer and whose great photosensitivity could be related to the chirality of EA molecules.

Key words: CRYSTAL STRUCTURE, ENANTIOMORPH, X-RAY DIFFRACTION ANALYSIS