Melchor G. Hernández

The 13C NMR spectra of some ent-18-hydroxykaur-16-enes

Abstract The 13 C NMR spectra are reported for thirteen ent -18-hydroxykaur-16-enes and their value for determining the C-4 stereochemistry is discussed.

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.

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.

Carotane sesquiterpenes from Ferula linkii

Abstract Four new carotane sesquiterpenes have been isolated from Ferula linkii. They have been identified as the 5-isovalerate of isolancerotriol, the 5-isovalerate and 5-angelate of isolancerotetrol, and the 5-isovalerate of epoxyisolancerotetrol.

Chemical ecology of canarian laurel forest: Toxic diterpenes fromPersea indica (Lauraceae).

The tree speciesP. indica (Lauraceae) is an important endemism in the Canary Islands laurel forest and can readily be distinguished by its defoliated appearance due to the seasonal action of wild rats (Rattus rattus), which eat the plant and become intoxicated. These observations and the phytochemical interest of this plant species led us to study the potentially toxic chemicals responsible for such action. We found that an ethanolic extract ofP. indica and its water fraction were toxic when injected into laboratory mice. The mice also died after ingestion of the stems and showed a significant preference for those extracted and rehydrated with an 8% aqueous extract solution when compared with the water control. Two compounds that have been isolated from the toxic fraction and identified by spectroscopic methods are the polyhydroxy pentacyclic diterpenes ryanodol and cinnceylanol. Possible ecological implications are discussed.

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)

Diterpenes from sideritis dendrochahorra and s. cystosiphon

Abstract A new diterpene, sidendrodiol (ent-16β,18-dihydroxykaur-11-ene), has been isolated from Sideritis dendrochahorra. From S. cystosiphon two new diterpenic esters, the 18-palmitate of epicandicandiol and the diacetate of epicandicandiol have been identified. The 13CNMR spectra of ent-16β-hydroxykaur-11-ene and ent-16β-hydroxykaurane derivatives have been assigned.

Siderin, a new coumarin from Sideritis canariensis

2 pages, 1 scheme.-- Part XXIII in the series “New Sources of Natural Coumarins”. For Part XXII see Anal. Quim.

The microbiological transformation of some ent-13-epi-manoyl oxide diterpenes by Gibberella fujikuroi

Abstract Incubation of ent -19-hydroxy-13- epi -manoyl oxide with Gibberella fujikuroi afforded ent -12α,19-dihydroxy-13 - epi -manoyl oxide and ent -7β, 12α, 19-trihydroxy-13 - epi -manoyl oxide, the first of which was transformed by chemical methods into varol ( ent -12α-hydroxy-13- epi -manoyl oxide). The incubation of ent -3β-hydroxy-13- epi -manoyl oxide (ribenol) with the same fungus gave the 12β-hydroxy, the 11β-hydroxy and the 11β,12β-dihydroxy derivatives of ribenol, the first of which was identical with varodiol.

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.