The crystal structure of 7-demethyl-6-methoxy-5,6-dihydrochelerythrine, (C21H19NO5) (I), a new alkaloid isolated from Z. nitidum, was determine by x-ray diffraction. The compound crystallizes in a monoclinic system, space group P21/c, with 4 mols. in a unit cell of a = 14.213(7), b = 17.347(3), c = 7.513(9) ? b = 101.40(13)? The structure has been refined by the full matrix least-squares method using 1876 unique reflections with I ?3s(I) and the final residual factors are R = 0.096 (Rw = 0.077).

Key words: ALKALOID, CRYSTAL STRUCTURE DETERMINATION, UNIT CELL, MATRICES, SPACE GROUPS, LEAST SQUARE METHODS, ZANTHOXYLUM NITIDUM