Charles R. Howell

Antimicrobial terpenoids of Gossypium: Hemigossypol, 6-methoxyhemigossypol and 6-deoxyhemigossypol

Abstract The sesquiterpenoid aldehydes, hemigossypol ( 1 a), 6-methoxyhemigossypol ( 1 b), and 6-deoxyhemigossypol ( 1 c), were isolated and identified from Verticillium -infected stele tissue of Gossypium barbadense . Structures were established by spectral (UV, IR, NMR, MS) evidence and chemical transformations. This is the first report of ( 1 b) and ( 1 c) in nature, and of NMR and m.p. data for crystalline pure ( 1 a). Compound ( 1 a) occurred in diseased stele tissues of all 21 Gossypium species examined and in the genera, Cienfuegosia , Gossypioides , Hampea , and Thespesia ; it was absent in three Hibiscus spp. Compound ( 1 b) occurred in the same taxa as ( 1 a), except that it was absent in species of two cytogenetic groups (A and B genome) of Gossypium . Compound ( 1 c) occurred in trace quantities, or was not detected, in most species; however, its distribution appeared to besimilar to that

Antimicrobial terpenoids of Gossypium: 6-methoxygossypol and 6,6′-dimethoxygossypol☆

Abstract The triterpenoid aldehydes, gossypol ( 1 ), 6-methoxygossypol ( 2 ) and 6,6′-dimethoxygossypol ( 3 ); and the sesquiterpenoid aldehydes, hemigossypol ( 4 ) and methoxyhemigossypol ( 5 ), were isolated from 1-week-old roots of Gossypium hirsutum and G. barbadense and identified. This is the first report of 2 and 3 in nature and of 4 and 5 from healthy roots. Compounds 2 and 3 also constituted 30% of the total terpenoid aldehydes in the seeds of 1 cultivar of G. barbadense , but occurred only in trace quantities in those of G. hirsutum . Spectral data (UV, IR, NMR, MS) and proof of structure for 2 and 3 are presented.

Effect of aging on flavonoid content and resistance of cotton leaves to verticillium wilt

Abstract Young (1 to 3 nodes from the apex) leaves of Acala 4–42 cotton plants resist infection by Verticillium dahliae , but become susceptible with increased age. This phenomenon is due to inhibition of fungal growth in young leaves. Resistant young leaves contain (+)-catechin, (+)-gallocatechin, isoquercitrin and condensed tannins in higher concentration than do older, susceptible leaves. Infection increases the concentrations of these compounds, especially in young leaves. (+)-Catechin prevents conidiation by V. dahliae at 5 × 10 −5 m and strongly inhibits mycelial growth above 1 × 10 −3 m . The concentration of (+)-catechin and (+)-gallocatechin found in resistant leaves is consistent with that required to strongly inhibit mycelial growth, whereas the concentrations found in older, susceptible leaves is much less inhibitory.

Naphthofuran precursors of sesquiterpenoid aldehydes in diseased Gossypium

Abstract Crude terpenoid fractions from stele tissues of Gossypium barbadense infected with Verticillium dahliae contained two prominent compounds that were nonaldehydic, but readily autooxidized to the terpenoid aldehydes hemigossypol and 6-methoxyhemigossypol. Spectral analyses, chemical studies, and comparisons with model compounds showed that these compounds were the sesquiterpenoids 3,4-dihydroxy-5-isopropy]-7-methy]-2H-naphtho[1,8-bc]furan (1a) and 3-hydroxy-5-isopropyl-4-methoxy-7-methyl-2H-naphtho[1,8-bc]furan (1b). The trivial names desoxyhemigossypol and desoxy-6-methoxyhemigossypol are proposed for (1a) and (1b). The sesquiterpenoid, previously isolated and named vergosin, is apparently desoxy-6-methoxyhemigossypol.

The X-ray crystal structure determination, and biosynthetic studies of the antibiotic, heptelidic acid

Abstract A sesquiterpene lactone isolated from Gliocladium virens, was identical to the antibiotic, heptelidic acid The complete structure of heptelidic acid, including the orientation of the epoxide ring was determined by single crystal X-ray defraction analysis. Feeding experiments with carbon-13 labeled acetate allowed complete assignment of the 13C-NMR spectrum and showed that trans, trans- or cis, trans-farnesyl pyrophosphate is the probable biosynthetic precursor to heptelidic acid. These experiments also showed that during the biosynthesis of cadalene type sesquiterpenes, the isopropylidene group is held rigid during ring closure and protonation. Thus, in the feeding experiment with [1,2-13C] acetate the methine carbon of the isopropyl group in heptelidic acid is asymmetric since the carbon of one methyl group is 13C and the other is 12C. An enzymatic Baeyer-Villiger type oxygen insertion is proposed for the formation of the lactone ring.