In order for the tert-Bu group to be sufficiently close to both and Hj in 1 and diacetate 3 (to account for NOE's), the cyclopentane ring must be puckered so that the tert-Bu is quasiequatorial,1' and of the two possible arrangements, tert-Bu cis or trans to Hh, only the trans arrangement can account for the observed JHf and JHG (ca. 7 Hz) (see 9; in the opposite configuration, the cyclopentane would be puckered downward1' and adopt a conformation in which these J values cannot be both large). The structure thus derived bears a striking resemblance to the diterpenoid ginkgolides, e.g., ginkgolide A, 10.12 The absolute configuration is based on that of the latter.la,eAcknowledgment. The work at Sendai was supported by the Ministry of Education, and USPHS Grant No. CA08394. We (R. T. M.) acknowledge with thanks support of the research by Mr. J. L. Pratt, and the structural advice and mass spectral-nmr measurements by Dr.
In connection with our investigations of SouthEast Asian plants,1) the roots of Psidium guaijava L. ("banjiro" or "banzakuro") from Taiwan were studied because of the reputed cancerostatic activity of this Chinese herb. Since the ether extract was an intractable mixture, it was first methylated; the ester was then chromatographed and recrystallized. This ester eventually turned out to be methyl arjunolate,2) the methyl ester of arjunolic acid (1).3,4) Preliminary chemical and spectroscopic studies carried out prior to its identification, however, disclosed a few points worthy of comment; these points will be reported below.Although the product obtained by the periodate oxidation of the ester 2 was analyzsed in the correct manner for a dialdehyde, it afforded only a mono-2, 4-dinitrophenylhydrazone, and its NMR spectrum showed only one aldehydic proton as a singlet (9.09 p.p.m.).
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