Diterpenoids chemical conversions

The chemistry of the diterpenoid alkaloids, rather than their structure elucidation by physical methods, has attracted more interest during the year covered by this Report. While several new alkaloids have been reported, most of the research on these polycyclic, polyfunctional bases has involved chemical conversions and synthetic methods. Most notably, Wiesner s group at New Brunswick, Canada, has reported a fourth-generation synthesis of the delphinine-type alkaloids. That this marvel of synthetic engineering accomplishes the stated goals1 of a highly efficient, fully regio- and stereo-specific synthesis of these complex natural products is abundantly clear. 

Chemical Conversion of Kobusine.—In their studies of diterpenoid interconversions, Okamoto and co-workers have reported the conversion of kobusine (113) into the amine (114) (Scheme 1). Chlorination of (114) with iV-chlorosuccinimide... 

Chemical Conversions of Kobusine.—Okamoto and co-workers have reported some of their recent studies of the chemistry of kobusine (74), a C-14-C-20-bridged atisine-type diterpenoid alkaloid. Since this bond constitutes a bicyclo-[3.2.1]octane system, and conversion into a double bond would violate Bredt s rule, there would appear to be no simple way to cleave it, Kobusine was reduced to (75) with sodium in n-propanol to protect the allylic alcohol. Acetylation of... 

Since e -16-kaurene (116) has been converted to phyllocladene, atisirene, and neoatisirene, the foregoing conversion also implies a formal chemical conversion of enmein to these diterpenoid hydrocarbons. 

Interconversions among Rabdosia diterpenoids have been frequently undertaken to establish the structures of new compounds, but were occasionally carried out as a matter of purely chemical interest. The following discussion is limited to interconversions between kaurene-type and 6,7-secokaurene-type diterpenes. The transformations are divided into biogenetic-type and retrobiogenetic-type chemical conversions. 

As the chemical conversion of enmein into several other naturally-occurring diterpenoids has been reported (see III and Scheme 39), this work also constituted a formal total syntheses of these natural products. 

Hashimoto. T K. Shiki, M. Tanaka, S. Takaoka, and Y. Asakawa, 1998b. Chemical conversion of labdane-type diterpenoid isolated from the liverwort Porella perrottetiana into ( ) amhrox. 9 ... 

Delectine.—A new diterpenoid alkaloid, delectine, has been isolated from Delphinium dictyocarpum7 This base, C31H44N2O8, m.p. 107—109 C, was shown to be the anthranilate ester (6) by chemical and spectral studies and by conversion into 00 -dimethyl-lycotonine (7). Acetylation of delectine gave an NO-diacetyl derivative (8). On alkaline hydrolysis of delectine, anthranilic acid and the alkamine (9) were obtained. Methylation of (9) with methyl iodide-sodium hydride gave (7), which was... 

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