68 訶子のタンニン

抄録

The structure of terchebin to which Ib was assigned previously in a literature, has been revised to VII, based on the data as follows. The PMR signals which were previously regarded as due to the protons at C_2, and C_3,, in Ib, are now assigned to those at C_1, and C_3, in VII, based on the analogy of these signals to those in geraniin. The CMR spectrum shows that the structure of the ester residue at O-2 and O-4 of glucose is analogous to that in geraniin, and therefore that Ib is excluded. The evidences of the stereostructure have been obtained by the analogy of the shifts in the PMR spectrum of III to those of the corresponding derivative of geraniin, and also by the optical property of VIII which was derived from III. The structure of terchebin is accordingly represented by VII. The structures of chebulinic acid and chebulagic acid, which were previously regarded as dicarboxylic acids, XI and XII^2, have been revised to monocarboxylactones, XIII and XIX, respectively, based on the following data. The DIS measurement of chebulinic acid and chebulagic acid showed dual peak for only one carboxyl carbon. The absence of DIS in the phenolic carbon, C_6,, indicates formation of a lactone between C_6,, and a carboxyl group in both of these tannins. The results of structural investigations of the methylated derivatives are also in agreement with structure XIII. An additional ellagitannin has been isolated from myrobalans, and identified as punicalagin.