Larry A. Calhoun

Isolation and characterization of phytotoxins associated with Streptomyces scabies

Two phytotoxins capable of inducing scab-like lesions on immature potato tubers were isolated from field grown and aseptically cultured potato tubers that had been infected by Streptomyces scabies; the compounds were characterized by spectral methods and partial syntheses as unique 2,5-dioxopiperazines.

Metabolites toxic to spruce budworm from balsam fir needle endophytes

The bioactive constituents of extracts of three strains of balsam fir endophytic fungi, reported to cause reduced growth rate and mortality of spruce budworm larvae, have been isolated and characterized. Bioassay-directed fractionation has resulted in the identification of heptelidic acid, 1,5a,6,7,8,9a-hexahydro-6-(1-methylethyl)-1-oxo-spiro[2-benzoxepin-9(3H),2′oxirane]-4-carboxylic acid ( 1 ), and two new analogues, heptelidic acid chlorohydrin ( 2 ), and hydroheptelidic acid ( 3 ), as the biologically active components of ? Phyllosticta sp. strain 76. The active component of Hormonema dematioides strains 53 and 143 was identified as (+)rugulosin ( 4 ), an anthraquinone previously reported to exhibit a wide spectrum of biological activity. This is the first report of the identification of toxins from fungal endophytes of woody plants.

Enniatins fromFusarium avenaceum isolated from balsam fir foliage and their toxicity to spruce budworm larvae,Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

Material extracted from hyphae ofFusarium avenaceum, isolated from foliage of balsam fir,Abies balsamea, was toxic to spruce budworm larvae when incorporated into insect diet. The major insecticidal component of the toxic fraction was identified by chemical and spectroscopic methods as enniatin complex, rich in enniatin A/A1. Possible ecological implications of these observations are considered.

Thermal desorption of hydrogen from ammonia borane: unexpected role of homopolar B–H⋯H–B interactions

The solid-state structure of ammonia borane is held together by an intricate N-H···H-B proton-hydride bonding network. These intermolecular interactions have long been considered to mediate the release of hydrogen from this material. Here we reveal the silent but important role played by B-H···H-B interactions in the thermal decomposition of this leading hydrogen storage candidate.

Sucrose esters associated with glandular trichomes of wild Lycopersicon species

Abstract Complexes of 2,3,4,1′-tetra- O - and 2,3,4-tri- O -acylated sucrose esters were identified as the major nonvolatile constituents in the exudate from glandular trichomes of Lycopersicon hirsutum and L. hirsutum f. sp. glabratum , respectively. The principal tetra- O -acylated ester was resolved by reversed phase HPLC and characterized as 2,4,1′-tri- O -(3-methylbutyryl)-3- O -(2-methylbutyryl)sucrose. A single 2,3,1′-tri- O -acylated sucrose ester was predominant in the exudate from the glandular trichomes of L. peruvianum var. glandulosum .

Isolation and characterization of 3,3′,4,6-tetra-O-acylated sucrose esters from the type B glandular trichomes of Solanum berthaultii Hawkes (PI 265857)

Abstract A series of polar, high-molecular-weight compounds that comprise the major portion of nonvolatile constituents in the exudate from type B glandular trichomes of S. berthaultii Hawkes (PI 265857) were isolated by silica gel t.l.c. and identified by spectroscopic and chemical means as a complex of 3,3′,4,6-tetra- O -acylated sucrose esters. Two of the principal sucrose esters were resolved by reversed-phase t.l.c. and characterized as 6- O -capryl-3,3′,4-tri- O -isobutyrylsucrose and 6- O -capryl-3′- O -isobutyryl-3,4-di- O -(2-methylbutyryl)sucrose.

3,4-Di-O-isobutyryl-6-O-caprylsucrose: the major component of a novel sucrose ester complex from the type B glandular trichomes of Solanum berthaultii hawkes (Pl 473340)

Evidence is presented that sucrose esters comprise the major portion of nonvolatile constituents in the exudate from type B glandular trichomes of Solanum berthaultii Hawkes (Pl 473340); the principal sucrose ester was characterized as 3,4-di-O-isobutyryl-6-O-caprylsucrose.

6 2,3-Di-O- and 1,2,3-tri-O-acylated glucose esters from the glandular trichomes of Datura metel

Abstract Complexes of 2,3-di- O - and 1,2,3-tri- O -acylated glucose esters were identified as the major non-volatile constituents in the exudate from type B glandular trichomes of Datura metel . The principal glucose esters were resolved by reversed phase TLC and characterized as 2,3-di- O -hexanoyl-α-glucopyranose and 1,2,3-tri- O -hexanoyl-α-glucopyranose.

Elucidation of structures for a unique class of 2,3,4,3′-tetra-O-acylated sucrose esters from the type B glandular trichomes of Solanum neocardenasii Hawkes & Hjerting (PI 498129)

Abstract A class of unique sucrose esters that comprise the greater portion of non-volatile constituents in the exudate from type B glandular trichomes of S. neocardenasii Hawkes & Hjerting (PI 498129) were resolved by reversed phase t.l.c. The major components were characterized by a combination of hydrolysis studies and spectroscopic techniques as 2-O-acetyl-3′-O-hexanoyl-3,4-di-O-isobutyryl-sucrose, 2-O-acetyl-3′,4-di-O-hexanoyl-3-O-isobutyrylsucrose, and 2-O-acetyl-3′-O-decanoyl-3,4-di-O-isobutyrylsucrose.

3,4-Di-O- and 2,3,4-tri-O-acylated glucose esters from the glandular trichomes of nontuberous Solanum species

Abstract Complexes of 3,4-di-O- and 2,3,4-tri- O -acylated glucose esters were identified as the major nonvolatile constituents in the exudate from type B glandular trichomes of certain nontuberous Solanum species. The principal glucose ester was resolved by reversed phase TLC and characterized as 2- O -acetyl-3- O -isobutyryl-4- O -isocaprylglucopyranose.