Braulio M. Fraga

Triterpene-based plant defenses

Pentacyclic triterpenes are abundant in the plant kingdom and have a wide array of pharmacological activities. They also have insect antifeedant effects and therefore apparently play a role in plant defense. In this paper, we describe the insecticidal activity of pentacyclic triterpenes of plant origin from different chemical classes on several insect pests (Spodoptera littoralis, Leptinotarsa decemlineata and Myzus persicae), their phytotoxic properties and their selective cytotoxic effects on insect-derived Sf9 and mammalian CHO cells. We also discuss the role they play in plant defense based on these activities.

Diterpenes from the roots of Salvia canariensis

Abstract The new diterpenes, deoxocarnosol 12-methyl ether, salvicanol and 6α-hydroxydemethylcryptojaponol, and the known ones, sugiol and demethylcryptojaponol, have been isolated from the bark of the roots of Salvia canariensis .

A chemotaxonomic study of nine Canarian Sideritis species.

Nine taxa of the Sideritis genus, Sideritis argosphacelus var. spicata, Sideritis candicans var. eriocephala,Sideritis discolor, Sideritis kuegleriana, Sideritis lotsyi, Sideritis lotsyi var. mascaensis, Sideritis marmorea, Sideritis soluta and Sideritis tenoi, which are endemic from the Canary Islands, have been chemically studied. The diterpene sicanatriol 7beta,18-diacetate was obtained from S. argosphacelus var. spicata, whilst a nor-diterpene, epiadejone, and the 3(2H)-benzofuranone solutin have been found in S. soluta. Another diterpene, sidendrodiol 18-monoacetate, has been isolated from S. argosphacelus var. spicata, for the first time as a natural product. Known sesquiterpenes, diterpenes, triterpenes, sterols, flavones, coumarins and other aromatic derivatives have also been isolated. These studies support the botanical division of the genus into two subgenera, Sideritis and Marrubiastrum, the three sections of the latter subgenus, Cretica, Empedocleopsis and Marrubiastrum, and the elevation of S. argosphacelus var. spicata, S. candicans var. eriocephala and S. lotsyi var. mascaensis to the rank of species.

Dehydroabietane diterpenes from Nepeta teydea

Abstract The new diterpenes dehydroabietan-18-ol acetate, teideadiol 18-monoacetate, teideadiol 18-malonate and teidic acid have been isolated from the aerial parts of Nepeta teydea . The known diterpenes dehydroabietan-18-ol (pomiferin A) and teideadiol have also been obtained from this species. The 13 C NMR spectra of several dehydroabietane derivatives have been assigned.

Biotransformation of the diterpene ribenone by Mucor plumbeus

Abstract The microbiological transformation of the diterpene ribenone (3-oxo-ent-13-epi-manoyl oxide) by the fungus Mucor plumbeus has been studied. Epoxidation of the vinyl group constitutes the main reaction and there exists a preference for hydroxylation at C-1(α), C-6(α or β) and C-12(β) and, to a lesser degree, at C-7(α) and C-11(β). Other observed reactions were the reduction of the 3-oxo group to a 3β-alcohol and the formation of metabolites with a 1,2-double bond. In this work the stereochemistry at C-14 of the diterpenes excoecarins A, B and C has been revised on the basis of X-ray data.

Nor-sesquiterpenes from Teucrium heterophyllum

A new sesquiterpene, 7-epi-teucrenone, and six novel nor-sesquiterpenes, teuhetone, teuhetenone A, teuhetenone B, tephyllone, 9β-hydroxy-tephyllone and 9-oxo-tephyllone, have been isolated from the aerial parts of Teucrium heterophyllum. This plant also contains the known terpene 3-oxo-α-ionol (3,4-dehydro-blumenol C)

The microbiological transformation of the diterpenes dehydroabietanol and teideadiol by Mucor plumbeus

The microbiological transformation of dehydroabietanol (18-hydroxy-dehydroabietane) by Mucor plumbeus led to 2alpha,18-dihydroxy-abieta-8,11,13,15-tetraene, 2alpha,15-dihydroxy-dehydroabietanol, 2alpha-hydroxy-15-methoxy-dehydroabietanol, 7beta-hydroxy-2-oxo-dehydroabietanol, 15-hydroxy-2-oxo-dehydroabietanol and 15,16-dihydroxy-2-oxo-dehydroabietanol, whilst that of teideadiol (1alpha,18-dihydroxy-dehydroabietane) gave 2alpha-hydroxy-teideadiol, 7alpha-hydroxy-teideadiol and 7beta-hydroxy-teideadiol. Thus, 2alpha- and 7beta-hydroxylation occur in both biotransformations and the 15-hydroxylation is inhibited in the biotransformation of teideadiol by the presence of a 1alpha-alcohol.

Phytochemistry and chemotaxonomy of Sideritis species from the Mediterranean region.

The phytochemical content of the Mediterranean species of the Sideritis genus has been reviewed. The components included in this review are monoterpenes, sesquiterpenes, diterpenes, triterpenes, sterols, flavones, coumarins and phenylpropanoids. From the chemotaxonomic point of view, we have divided the species from this region into four groups. The first of this is formed by taxa containing triterpenes, but not diterpenes. A second group is constituted by species having bicyclic diterpenes of the labdane type and not diterpenes. The third group is characterized by its content in tetracyclic diterpenes of the ent-kaurene type. A fourth group is composed of plants with tetracyclic diterpenes of the ent-beyer-15-ene and/or ent-atis-13-ene class. In addition, the relations of these Mediterranean species with those of the Macaronesian region have been examined.

Antifeedant Activity of Fatty Acid Esters and Phytosterols from Echium wildpretii

Crude extracts and fractions from Echium wildpretii H. Pearson ex Hook. f. subsp. wildpretii (Boraginaceae) have been tested against insect species Spodoptera littoralis, Leptinotarsa decemlineata, and the aphids Myzus persicae, Diuraphis noxia, Metopolophium dirhodum, Rhopalosiphum maidis, and Rhopalosiphum padi. The EtOH extract and the lipid and steroidal fractions of E. wildpretii exhibited significant antifeedant activities against the aphids and L. decemlineata. Two bioactive mixtures composed of fatty acid esters and n‐alkanes were obtained from the lipid fraction. The bioguided fractionation of the steroidal fraction resulted in the isolation of glutinol, β‐sitosterol, (3β,7α)‐stigmast‐5‐ene‐3,7‐diol, and (3β,7α)‐7‐methoxystigmast‐5‐en‐3‐ol. The latter two compounds exhibited potent antifeedant activities against L. decemlineata indicating that the presence of an O‐bearing C(7) was responsible for the activities of these molecules.

Minor diterpenes from Persea indica: their antifeedant activity

The new diterpenes anhydrocinnzeylanone, garajonone and 2,3-didehydrocinnzeylanone, and the known anhydrocinnzeylanine, have been isolated from Persea indica. The antifeedant activity of these compounds has been evaluated showing the importance of the 11-hemiketal group for the antifeedant effects of ryanodane diterpenes.