The molecular geometry of asiaticoside (1 ), a trisaccharide triterpene isolated from Centella asiatica, has been determined by a single-crystal X-ray analysis. The glycoside, C,H,,O,,, is prismatic with space group monoclinic, C2 and lattice constants a = 41.46 (1 ), b = 7.563 (4), c = 17.988 ( 5 ) . A, p = 99.66(5)", cell volume V = 5 602.3 A3, and Z = 4. Diffractometer intensity measurements were made with Cu-K, radiation and least-squares adjustment of the atomic parameters converged t o a final R value of 0.073. 13C N.m.r. and f.a.b.-m.s. are satisfactorily interpreted within terms of the structure.Centella asiatica Linn. (syn. HydrocotyZ asiatica Linn.) (Umbelliferae) is a prostrate, perennial, faintly aromatic herb found wild throughout India. The plant enjoys a considerable reputation in Indian medicine as a diuretic and tonic. An infusion of the plant is used in India and Madagascar in the treatment of leprosy.' The major glycoside, asiaticoside, is known to have antileprotic a ~t i v i t y . ' ~ Phytochemical studies5-* and elucidation of the planar structure of asiaticoside have been reported.g* '' However, the complete stereochemistry remains to be established. In view of the potential of this glycoside in the treatment of leprosy we now report the single-crystal Xray determination of the complete structure and stereochemistry of asiaticoside together with 13C n.m.r. and fast-atom-bombardment mass spectra (f.a.b.-m.s.).' '-' to the xenon gun with 1-thioglycerol (for negative-ion f.a.b.) or diethanolamine (DEA) (for positive-ion f.a.b.) as matrices. G = Glucose, R = rhamnose. a,b*c May be interchanged in each vertical column.
X-ray small-and medium-angle scattering of partially ordered or semicrystalline materials is composed of background scattering from the form scattering of the components and from the amorphous phase and of peaks from the scattering of the crystallites. By the slit geometry of X-ray diffractometers constructed for registration of small-and medium-angle X-ray scattering, the diffuse scattering and the peaks are distorted and the peak positions and half-widths are changed. A program module based on the Akima interpolation [Akima (1970). J. Assoc. Comput. Math. 17,[589][590][591][592][593][594][595][596][597][598][599][600][601][602] is proposed for calculation of the first derivative of the complete smeared scattering curve, which is then explicitly used in direct collimationcorrection procedures. The desmearing of scattering curves from semicrystalline starch samples proves the convenience of the method for low-noise conditions and exhibits a significant gain of measuring time in comparison with data of comparable accuracy but measured with SoUer-slit collimation systems or desmeared with direct methods using frequency filtering.
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