CRYSTAL STRUCTURE OF THE TANNIN GERANIIN BASED ON CONVENTIONAL X-RAY AND ON SYNCHROTRON DATA. Peter Luger, Manuela Weber, Freie Universität Berlin, Germany; Setsuo Kashino, Yoshiaki Amakura, Takashi Yoshida, Takuo Okuda, Okayama University, Japan; Gezina Beurskens, University of Nijmegen, The Netherlands; Zbigniew Dauter, EMBL Outstation c/o DESY, Hamburg, Germany

Geraniin, C₄₁H₂₈O₂₇ x 7H₂O,the main tannin from Geranium thunbergii Sieb. et Zucc. is one of the most popular folk medicines and also an official antidiarrhetic in Japan. Conventional X-ray diffractometer data at room temperature and room and low temperature (120K) synchrotron data (beam line X 1 1 at EMBL/DESY Hamburg with a MARRESEARCH imaging plate) were measured.The structure could not be determined with any of the currently distributed direct methods programs but was easily solved with DIRDIF using several conformers of the hexahydroxydiphenoyl group as input fragment into a vector search. Thus a 20 atom fragment was sufficient to solve this 75 (non H)atoms problem. A molecular structure was established where a cyclohexenetrione moiety attached to O-4 of a central glucose unit was in a hydrated six-membered hemiacetal-ring structure as expected from a solid state NMR study. Due to the high oligocyclic substitution the glucopyranosyl ring is in the unusual ¹C₄ conformation. Refinement of the low temperature synchrotron data allowed the identification of almost all hydrogens even at the seven water molecules so that a rather complex system of about thirty different hydrogen bonds can be studied in some details.