A.G. González

Three triterpenes and other terpenoids from Catha cassinoides.

Abstract The investigation of stems and leaves of Catha cassinoides afforded, in addition to sitosterol, β-amyrin, ursolic acid, lup-20(29)-en-3β,30-diol and friedelin, three new pentacyclic triterpenes: 30-hydroxyfriedelan-3-one, 29-hydroxyfriedelan-3-one and 3-oxo-friedelan-29-oic acid. The structures ofthese were determined by spectral studies and correlations, and were confirmed by X-ray analysis of 29-hydroxyfriedelan-3-one acetate.

Terpenoids of the red alga laurencia pinnatifida

Abstract The structures of three brominated terpenoids which are natural products from the red alga Laurencia pinnatifida (Gmal. Lamour) are described. The structures of the sesquiterpenes 4 and 5 were determined by spectral comparison and chemical interconversion. The structure of the squalene-derived terpenoid 8 was secured by chemical transformation into thyrsiferol, a brominated triterpene previously isolated from the red alga Laurencia thyrsifera.

Deacylation of aromatic acetates. A new method of selective protection of the hydroxyl function.

Abstract Acetoxyaromatic compounds are selectively deacylated, via a catalytic-type reaction, to the corresponding phenolic derivatives, by treatment uith activated zinc in methanol.

Biomimetic approach to the synthesis of rhodolaureol and rhodolauradiol

Abstract It is postulated that 9-hydroxy-β-iso-obtusene ( 4 ) is the biogenetic precursor of the tricyclic sesquiterpenoids rhodolauradiol ( 7 ) and rhodolaureol ( 9 ). The transformation 4 → 7 was carried out under non-enzymic conditions.

Diterpenoids of mixed biogenesis in phaeophyta biogenetic-type interconversions☆

In the course of research into marine natural products, the diterpenoids taondiol 10 and atomaric acid 15, were isolated from the brown seaweed Taonia atomaria. The similarities of these structures plus the fact that both compounds come from the same alga suggest that there may be a biogenetic relationship between the two. This speculated relationship is adumbrated in Scheme 1, where the cyclic and acyclic diterpenoids of mixed biogenesis isolated from Phaeophyta are interrelated. In the present work, the competitive cyclisation of the proposed olefinic intermediate 4 to the naturally occurring compounds taondiol 10, isotandiol 11, epitaondiol 12 and stypodiol 13, is reported. The stereoselective transformation of atomaric acid 15 into the compound 4 is also reported, which transformation occurs by intramolecular carbocylisation of the olefinic aldehyde 7 followed by backbone rearrangement to the olefin 4. This result prompted the proposal that atomaric acid 15 may arise in nature by means of a like rearrangement but operating in a reverse direction.

Carbon-13 NMR application to Laurencia polyhalogenated sesquiterpenes☆

By examining the chemical shifts of the carbons involved in vicinal trans-bromo-chloro systems, which are frequently isolated from Laurencia sesquiterpenes, it is possible to establish the position of the Br and Cl atoms beyond a doubt. This method was used in the structure determination of the new terpenoids, obtusane 3) and isofurocaespitane (17).

Chlorohyssopifolin C, D, E and vahlenin, four new sesquiterpene lactones from Centaurea hyssopifolia☆

Abstract On the basis of chemical and spectroscopic evidence, structures are assigned to four new sesquiterpene lactones: chlorohyssopifolin C, D and E (guaiano

A new diterpene fromAplysia dactylomela

Abstract From the digestive gland of the sea hare Aplysia dactylomela a new trioxygenated diterpene possessing the dolabellane skeleton was isolated. The structure was solved by spectral properties and X-ray diffraction analysis.

Isocaespitol, a new halogenated sesquiterpene from Laurencia caespitosa

Abstract The halogenated sesquiterpene isocaespitol ( 1 ) has been isolated from the marine alga Laurencia caespitosa Lamx and its structure determined by X-ray crystallography.

X ray study of sesquiterpene constituents of the alga L obtusa leads to structure revision

Abstract L obtusa sesquiterpenes were subjected to an x ray analysis in orde to determine definitively the position of the Br and Cl atoms. As a result some previously-published structures 2 had to be revised.