A new depsidone from the neotricone-rich chemotype of the lichenised fungus Usnea fulvoreagens.

Individuals of Usnea fulvoreagens (Parmeliaceae, lichenised Ascomycota), a shrubby corticolous species that is widespread in Europe, East Asia and North America, produce medullary lichen acids in several distinct chemotypic patterns. One such chemotype reportedly contains an unidentified substance as the major secondary metabolite. We isolated this compound from Californian specimens of U. fulvoreagens and identified it as the rare depsidone neotricone. A co-occurring compound, conneotricone, was identified as 4,10-dihydroxy-5-(hydroxymethyl)-8-methyl-3,7-dioxo-1,3-dihydro-7H-isobenzofuro[4,5-b][1,4]benzodioxepine-11-carboxylic acid by NMR and HPLC-UV-MSn comparison with the material synthesised from salazinic acid.

NMR structural characterization from one-bond 13 C13 C couplings: Complete assignment of a hydrogen-poor depsidone.

The connectivity, conformation, tautomeric form, and dynamics of a new depsidone (perisalazinic acid) were characterized using one-bond 13 C13 C NMR scalar couplings (1 JCC ) obtained from the INADEQUATE experiment. Characterization of perisalazinic acid using more conventional NMR techniques is problematic due to the extremely limited number of CH protons present. In the present study, 81 candidate structures were considered and a best fit structure was selected by comparing computed 1 JCC values for each candidate to 15 experimental values. Of the six flexible moieties in perisalazinic acid, three are adequately represented by a single orientation stabilized by intramolecular hydrogen bonding. The three remaining groups are present as mixtures of conformers with two sites consisting of a pair of conformations and another disordered over six orientations. This study demonstrates the feasibility of complete three-dimensional structural characterization of an unknown using only theoretical and experimental 1 JCC values.

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and ß-Isothapsenol.

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and ß-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and ß-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, 1H and 13C chemical shifts, and interconversion pathways.

Irregular sesquiterpenoids from Ligusticum grayi roots.

Root oil of Ligusticum grayi (Apiaceae) contains numerous irregular sesquiterpenoids. In addition to the known acyclic sesquilavandulol and a sesquilavandulyl aldehyde, two thapsanes, one epithapsane, and 14 sesquiterpenoids representing eight hitherto unknown carbon skeletons were found. These skeletons are: prethapsane, i.e. 1,1,2,3a,7,7-hexamethyloctahydro-1H-indene; isothapsane, i.e. 1,2,3a,6,7,7a-hexamethyloctahydro-1H-indene; ligustigrane, i.e. 1,1,2,7,7,7a-hexamethyloctahydro-1H-indene; isoligustigrane, i.e. 1,1,2,6,7,7a-hexamethyloctahydro-1H-indene; preisothapsane, i.e. 1,1,2,3a,6,7-hexamethyloctahydro-1H-indene; isoprethapsane, i.e. 1,1,2,4,7,7-hexamethyloctahydro-1H-indene; allothapsane, i.e. 1,1,2,3a,7,7a-hexamethyloctahydro-1H-indene; and oshalagrane, i.e. 1,1,2,4,6,6-hexamethylspiro[4.4]nonane. The bicyclic sesquiterpenoids are presumably biosynthesized by head-to-head coupling of geranyl diphosphate and dimethylallyl diphosphate, followed by a cyclization sequence leading to a hydroindane skeleton with six one-carbon substituents. Subsequent rearrangements--primarily methyl migrations--account for the remarkable variety of structures represented in L. grayi root oil.

Cuticular hydrocarbons and soldier defense secretions of Reticulitermes in southern California: a critical analysis of the taxonomy of the genus in North America.

Cuticular hydrocarbons (CHC) and soldier defense secretions (SDS) were characterized for collections of Reticulitermes from six counties (Los Angeles, Orange, Riverside, San Bernardino, San Diego, and Santa Barbara) in southern California. Collection sites included the type locality for R. hesperus, Lake Arrowhead (formerly known as Little Bear Lake) in the San Bernardino Mountains. In southern California, there are two CHC phenotypes, SC-A and SC-B, which are easily distinguished by the presence or absence of 5-methyl pentacosane, 5-methyl heptacosane, 5,17-dimethyl pentacosane, and 5,17-dimethyl heptacosane. These phenotypes are similar, but not identical, to previously designated phenotypes of Reticulitermes from northern California. The SDS of termites collected from southern California were characterized; (-)-germacrene A was abundant in all but the four samples from Lake Arrowhead. Soldiers of phenotype SC-A produced >79% germacrene A. The four samples from Lake Arrowhead produced no germacrene A, but contained >78% gamma-cadinene. The SDS from the Lake Arrowhead samples were more similar to those of CA-A/CA-A' from northern California than to any of the CHC phenotypes from southern California. Soldiers of CHC phenotype SC-B produced germacrene A, with the proportion varying from 16.2 to 98.7%. The SDS of SC-B were more similar to those of SC-A than to any of the phenotypes from northern California. The CHC phenotype SC-A found in southern California likely represents R. hesperus and SC-B appears to be a new, as yet undescribed species. We discuss the state of current taxonomic research on Reticulitermes.

Sesquiterpenes from Cupressus macrocarpa foliage.

Ten sesquiterpenes, many with unusual carbon skeletons, were identified in foliage of Cupressus macrocarpa. These are (-)-10-epi-beta-acoradiene; ent-widdra-2,4(14)-diene; (E)-iso-gamma-bisabolene, i.e., (4E)-4-(1,5-dimethylhex-5-enylidene)-1-methylcyclohexene; (-)-cumacrene, i.e., (4S)-4-[(1R,2S)-2-isopropenyl-1-methylcyclobutyl]-1-methylcyclohexene; (-)-alpha-chamipinene, i.e., (1S,6S,7S)-2,2,6,8-tetramethyltricyclo[5.3.1.01,6]undec-8-ene; and five sesquiterpenes with a 3,3,4'-trimethyl-1,1'-bi(cyclohexyl) skeleton for which the trivial name macrocarpane is proposed. The possible single-enzyme biogenesis of these sesquiterpenes is discussed.

A pregeijerene isomer from Juniperus erectopatens foliage.

A hydrocarbon that is widespread in Juniperus foliage was isolated from Juniperus erectopatens (Cheng and L. K. Fu) R. P. Adams and identified as (E,E,E)-1,7-dimethylcyclodeca-1,4,7-triene (pregeijerene B). Geometry of the disubstituted double bond was determined by IR and NMR spectroscopy, while that of the trisubstituted double bonds was proven by comparison of the products of selective hydrogenation of the title compound and of pregeijerene. Common biosynthesis of pregeijerene B and a germacrane sesquiterpenoid, 8alpha-acetoxyhedycaryol, is inferred from their co-occurrence in foliage of 24 Juniperus species.