Antonio G. González

Structure and absolute configurations of Dictyota sp. diterpenes

Eight diterpenes belonging to the dolostane carbon skeleton have been isolated from the Canary Island brown alga Dictyola sp. The structures including absolute configuration of these diterpenes were secured by X-ray analysis of the triol derivative 7 followed by chemical interconversions.

Bioactive humulene derivatives from Asteriscus vogelii

The bioactive fractions obtained from the extract of Asteriscus vogelii afforded a new humulene derivative, the 8-oxo-6,7,9,10-tetrahydrohumulen-1,12-olide (1), in addition to the known asteriscunolides A (2), C (3) and D (4), and the acids 8-oxo-alpha-humula-6Z,9Z-dien-12-oic acid (5), 8-oxo-alpha-humula-6E,9Z-dien- 12-oic acid (6) and 8-oxo-alpha-humula-6E,9E-dien-12-oic acid (7), characterized as their methyl esters. Evaluation of their phytotoxic and cytotoxic activities was accomplished. Compounds 3 and 4 gave the highest inhibition of plant cell cultures and of the plant Lemna paucicostata. Compound 4 was also the most active against P-338 lymphoma in mice, A-549 carcinoma of human lung, HT-29 carcinoma of human colon and MEL-28 human melanoma.

A facile chemoselective deacetylation in the presence of benzoyl and p-bromobenzoyl groups using p-toluenesulfonic acid

Abstract The acetyl group was chemoselectively cleaved in the presence of p -toluenesulfonic acid ( p -TsOH) in CH 2 Cl 2 /MeOH without affecting the benzoyl (benzoate and p -bromobenzoate) groups and no transesterification product was observed. The treatment of protected carbohydrates with p -TsOH·H 2 O at room temperature usually required a longer reaction time than at 40°C. Other types of sulfonic acid such as 10-camphorsulfonic (CSA) led to similar results.

Two new diterpene alkaloids from delphinium cardiopetalum DC

Chemical, spectral and X ray data are given for cardiopetaline and cardiopetalidine, two new C-19 diterpene alkaloids from the genus Delphinium.

Flavans of dragon’s blood from Dracaena draco and Dracaena tamaranae

Abstract Flavans of D. draco subsp. draco and subsp. ajgal and of D. tamaranae were isolated and identified for a chemotaxonomic survey. A major constituent of all taxa was (2 S )-4,7′-dihydroxy-8-methylflavan.

Two new polyhalogenated monoterpenes from the red alga Plocamium cartilagineum

Abstract The structures and absolute configurations of two new halogenated alicyclic monoterpenes isolated from the ether extract of the red alga Plocamium cartilagineum (Linn) Dixon were determined as: 1 R ,2 S ,4 S ,5 R -5-chloro-2- E -chlorovinyl-1,4-dibromo-1,5-dimethylcyclohexane and 1 S ,2 S ,4 R ,5 S -2-bromo-1- E -bromovinyl-4,5-dichloro-1,5-dimethylcyclohexane, respectively.

The microbiological transformation of some ent-kaur-6, 16-dienes by Gibberella fujikuroi

Abstract The preparation of ent -kaur-6, 16-diene and ent - 18-hydroxykaur-6, 16-diene from epicandicandiol and of ent -3β, 18-dihydroxykaur-6, 16-diene from foliol is described. On incubation with Gibberella fujikuroi ent -kaur-6, 16-diene gave 7-hydroxykaurenolide and 18-hydroxykaur-6, 16-diene afforded 7, 18-dihydroxykaurenolide, whilst ent -6α,7α-epoxy-3β,18-dihydroxykaur-16-ene was obtained from ent -3β,18-dihydroxykaur-6,16-diene. The possible biosynthetic significance of the 6, 7-epoxidation in kaurenolide formation is noted.

Lignans from Apollonias barbujana

Abstract Two new lignans, 2,3- bis [(4-hydroxy-3,5-dimethoxyphenyl)-methyl]-1,4-butanediol and demethylpiperitol, together with three already-known ones, have been isolated from the leaves of Apollonias barbujana (Lauraceae). The structures were fully characterized by spectroscopical methods. The known lignans were identified as sesamin, syringaresinol and the neolignan, dihydro-dehydrodiconiferyl alcohol.

Eupatarone, A 2-acetylbenzofuran from Eupatorium sternbergianum

Abstract A new benzofuran, eupatarone, together with 2-hydroxy-4, 5-dimethoxybenzaldehyde, 12-hydroxy-2, 3-dihydroeuparine, spathulenol, precocene II, dammaradienol, dammaradienol acetate, 5, 3′-dihydroxy-7, 4′-dimethoxyflavanone and 5, 7-dihydroxy-4′-methoxyflavanone, have been isolated from aerial parts of Eupatorium sternbergianum .

Carbon-13 nmr spectra of some ent-rosane diterpenoids

We thank Miss M. D. Casado and Miss M. Plaza for recording the 13C and 1HNMR spectra and Mr. J. Prieto for elemental analyses. This work was supported in part by the Comision Asesora de Investigacion Cientifica y Tecnica.