7α-Acetoxydihydronomilin: isolation, spectra, and crystal structure

Abstract

Methanol extraction of the ground seeds of Uncaria Gambier Roxb. followed by chromatography afforded a crystalline C30H38O10 terpene. This has been shown by X-ray analysis to be 7α-acetoxydihydronomilin. The crystals are orthorhombic, P212121, a = 13.158(2), b = 17.092(2), c = 12.689(2) Å, Z = 4, dx = 1.300, do = 1.300 g cm−3. The structure has been determined by the direct method and Fourier syntheses, and refined by block-diagonal least-squares to R = 0.042 for 2621 observed reflexions. The molecule contains a seven-membered lactone ring A, three six-membered rings B, C, D, a three-membered ring E, a furan ring F, and two acetate groups. A and B are chair, C is twist-boat, D is 1,3-diplanar, while E and F are planar. The A/B, A/C, C/D junctions are trans, D/E is cis, and F is linked to D by an equatorial C—C bond. The two acetate groups are in axial positions on A and B and are cis to each other. The O atom forming the apex of the three-membered ring is wedged between two H atoms and their parent C atoms at short intramolecular distances O … H = 2.28(2) and 2.28(3), and O … C = 2.623(3) and 2.668(4) Å. No intermolecular hydrogen bonding is indicated.