Diterpenes from Coleus forskohlii (WILLD.) BRIQ. (Labiatae).
Three new minor labdane diterpene glycosides, forskoditerpenoside C, D, and E (1-3), and a novel labdane diterpene forskoditerpene A (4) were isolated from the ethanol extract of the whole plant of Coleus forskohlii. Their structures and relative stereochemistry were elucidated on the basis of extensive spectroscopic analyses including 1D-, 2D-NMR, and HR-ESI-MS experiments. Compounds 1-3 showed an unusual 8,13-epoxy-labd-14-en-11-one glycoside pattern. They showed relaxative effects on isolated guinea pig tracheal spirals in vitro. Compound 4 with a cyclopropyl, confirmed by a single-crystal X-ray diffraction determination, is the first known labdane derivative with a spiro element.
Isolation, structure elucidation and synthesis of 1-deoxyforskolin
Abstract Isolation and structure elucidation of 1-deoxyforskolin ( 2 ), a minor forskolin related constituent, of the Indian herb Coleus forskohlii are described. The structure of 2 is confirmed by the 9-hydroxylation of 1,9-dideoxyforskolin ( 4 ).
A total synthesis of ( )-fumagillin.
fumagillin. The biological activity and novel structure of fumagillin have stimulated the interest of several groups in synthesis. However, the complications of asymmetry (six centers) and highly reactive functionality have conspired to prevent solution of the p r ~ b l e m . ~ The goal of this synthesis was (*)-fumagillol (2), since this should be easily convertible to fumagillin. In fact, treatment of (-)-fumagillol, readily available by degradation of fumagilliq6 with 1 equiv of methyllithium, followed by addition of this solution to 5 equiv of decatetraenedioyl chloride in tetrahydrofuran at 78', gave fumagillin, identical with natural fumagillin by thin-layer chromatographic (tlc), infrared (ir), nuclear magnetic resonance (nmr), and mass spectral comparison. The demonstration of the first total synthesis of (&)fumagillol proceeded as follows. Alkylation of methyl acetoacetate with 3,3-dimethylallyl bromide' followed by deacetylation using the procedure of Ritter and KanieckP gave methyl 5-methyl-4-hexenoate (3),9 bp 47-50' (5 mm) (57 % yield). Oxidation of the olefin 3 with selenium dioxide in 97 % aqueous 1,2-dimethoxyethane for 8 hr at reflux gave stereoselectively in 41 %