Abstract
Paucin (1c), a pseudoguaianolide glucoside, has been studied by X-ray diffraction and the glucose ring shown to be acetylated at position 6′-O. The sesquiterpenoid cycloheptane ring adopts a twist-boat conformation, while the cyclopentanone and α-methylene γ-lactone rings have half-chair and envelope conformations, respectively. The CC–CO and Cα–Cβ–Cγ–O torsion angles of the α-methylene γ-lactone are –10 and –17°. Crystals of paucin monohydrate are monoclinic, space group P21, with a= 18.308(4), b= 6.724(2), c= 9.987(4)A, β= 93.38(4)°, and Z= 2. The crystal structure was elucidated by direct-phasing methods and the atomic parameters were subsequently adjusted by least-squares calculations which converged at R 7.9% over 1 929 diffractometer reflections.
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