STRUCTURE OF THE TANNIN GERANIIN BASED ON CONVENTIONAL X-RAY DATA AT 295 K AND ON SYNCHROTRON DATA AT 293 AND 120 K

Geraniin, C41H28O27.7H(2)O, is the main tannin from Geranium thunbergi i Sieb. et Zucc., which is one of the most popular folk medicines and also an official antidiarrheic drug in Japan. Conventional X-ray diffr actometer data at 295 K and synchrotron data at 293 and 120 K (at EMBL /DESY Hamburg with a MARRESEARCH imaging plate) were measured. The str ucture could not be determined with any of the currently distributed d irect-methods programs, but was easily solved with DIRDIF using severa l conformers of the hexahydroxydiphenoyl group as input fragments into a vector-search procedure. A molecular structure was established wher e a cyclohexenetrione moiety attached to O4 of a central glucose unit was in a hydrated six-membered hemiacetal ring structure, as expected from the NMR study of crystalline geraniin. Owing to the high oligocyc lic substitution the glucopyranosyl ring is in the unusual C-1(4) conf ormation. Refinement of the low-temperature synchrotron data allowed i dentification of almost all the H atoms, even within the seven water m olecules, so that a rather complex system of approximately 30 differen t hydrogen bonds can be studied in some detail.