CHEMICAL INVESTIGATION OF BAO GONG TENG (ERYCIBE OBTHSIFOLIA BENTH) Ⅱ. THE STRUCTURE OF BAO GONG TENG A——A NEW MYOTIC AGENT

The chemical structure of Bao Gong Teng A, a new myotic agent isolated from the stem of Chinese medicinal plant Bao Gong Teng (Erycibe obtusifolia Benth.), has been determined by the analysis of ¹H and ¹³C NMR and high resolution MS data of Bao Gong Teng A and its derivatives. The functional groups present in the molecule of Bao Gong Teng A are a secondary amino group, a secondary alcoholic group and an acetoxy group. No double bond is present. By comparing the MS and ¹H NMR data of its N-methyl derivative to those of the authentic samples of 3α-and 3β-isomers of 6β-acetoxy-3-tropanol, it is certain that the molecule has nortropane skeleton with a 6β-acetoxy group. The position of the hydroxyl group can be assigned to C-2 by using the double resonance techniques in ¹H NMR of its N-methyl acetyl derivative. Furthermore, according to the base widths of proton signals the steric orientation of C-2 OH is possible only if it assumes a β-configuration in the favored chair form of piperidine. Consequently, the chemical structure of Bao Gong Teng A is represented as 2 β-hydroxy-6β-acetoxy-nortropane with a levorotation α_D²⁸ =-7.21 (C 0.97, H₂O). The explanation of all the principal fragments in its high-resolution mass spectra by such a structure is satisfactory.It is noteworthy that a strong myotic property is associated with the structure of natural tropane alkaloids of which some are known to have opposite mydriatic property and, to our knowledge, the structure and functions of Bao Gong Teng A have not been reported in the literature. This finding may have significance in the study of receptor theory in pharmacology.