Malcolm S. Kemp

Phytoalexins and stress metabolites in the sapwood of trees

Abstract A wide range of organic compounds, many of them fungitoxic or fungistatic, appear in the sapwood of trees after wounding, injury or fungal attack. There is evidence that most of these compounds are formed by dying parenchyma cells and they therefore can be considered to be phytoalexins. In many cases such compounds accumulate in narrow ‘reaction zones’ which serve to impede further progress of pathogens.

(−)-7-HYDROXYCALAMENENE, A PHYTOALEXIN FROM TILIA EUROPEA

Abstract The antifungal sesquiterpene (−)-7-hydroxycalamenene has been isolated and identified in Tilia europea (European Lime) infected with the fungus Ganoderma applanatum . It was found in the narrow pigmented boundary zone between healthy and infected wood.

Sesquiterpene phytoalexins from Ulmus glabra

Abstract Inoculation of Wych elm ( Ulmus glabra ) with the fungi Ceratocystis ulmi , Chrondrostereum purpureum and Coriolus versicolor induced the formation of a series of antifungal cadinane-type sesquiterpenes.

Debneyol, a fungicidal sesquiterpene from tnv infected Nicotiana debneyi

Abstract An antifungal sesquiterpene diol, debneyol, has been isolated from tobacco necrosis virus-inoculated leaves of Nicotiana debneyi and a structure is proposed from chemical, spectroscopic and biogenetic evidence. In contrast to the related phytoalexin capsidiol which is fungistatic, debneyol appears to exhibit genuine fungicidal activity.

Isolation, structure determination, and total synthesis of the dibenzofurans α- and β-pyrufuran, new phytoalexins from the wood of Pyrus communis L.

The antifungal compounds α- and β-pyrufuran have been isolated from the wood of perry pear trees [Pyrus communis L. (Rosaceae), cv. Hendre Huffcap) infected with Chondrostereum purpureum(Pers. ex Fr.) Pouzar, the causative fungus of silver leaf disease. Spectroscopic and chemical evidence show that the compounds are 1,2,3,4-substituted trimethoxydibenzofuranols. Three of the four possible positional isomers, compounds (11), (12), and (13), have been synthesized by cyclisation of the corresponding trimethoxydiphenyl ethers using palladium(II) acetate, followed by oxidation of the organo-lithium derivative using lithium t-butyl peroxide. The latter stage proved unsuccessful in the attempted synthesis of 2,3,4-trimethoxydibenzofuran-1-ol (10). Comparison of spectroscopic and chromatographic properties of the natural products and synthesized compounds show α-pyrufuran and β-pyrufuran to be 1,3,4-trimethoxydibenzofuran-2-ol (11) and 1,2,4-trimethoxydibenzofuran-3-ol (12), respectively.

Isolation and structure determination of γ-pyrufuran, a third induced antifungal dibenzofuran from the wood of Pyrus communis L. infected with Chondrostereum purpureum(Pers. ex Fr.) Pouzar

The induced antifungal compound γ-pyrufuran has been isolated from the wood of perry pear trees [Pyrus communis L. (Rosaceae) cv. Thorn.] infected with Chondrostereum purpureum(Pers. ex Fr.) Pouzar. Spectroscopic and chemical evidence indicate that the compound is one of four 1,2,3,4,7-substituted trimethoxydibenzofurandiols in which one hydroxy group occupies the 7-position. Selective reduction of the dimesylated derivative by hydrogen with a Pd–C catalyst, followed by base-catalysed hydrolysis, produced α-pyrufuran (1,3,4-trimethoxydibenzofuran-2-ol)(6), and shows γ-pyrufuran to be 1,3,4-trimethoxydibenzofuran-2,7-diol (1).

Cyclodebneyol, a fungitoxic sesquiterpene from TNV infected Nicotiana debneyi

Abstract A fungitoxic sesquiterpene alcohol, cyclodebneyol, has been isolated from tobacco necrosis virus inoculated leaves of Nicotiana debneyi. A structure is proposed from a comparison of its 13C and 1H NMR spectra with those of the closely related sesquiterpene, debneyol.

Isolation and structure determination of cotonefuran, an induced antifungal dibenzofuran from Cotoneaster lactea W.W.Sm

An antifungal compound, cotonefuran, has been isolated from necrotic wood of a fungal-infected specimen of Cotoneaster lactea W.W.Sm. (Rosaceae). Spectroscopic evidence demonstrates that cotonefuran is a trimethoxydibenzofurandiol which is trisubstituted in one aromatic ring and disubstituted in the other. Comparison of the 1H n.m.r. spectrum with the 1H n.m.r. spectra of suitable model dibenzofurans provided some information on the positioning of the substituents, but an X-ray analysis was necessary for a full structural elucidation. Cotonefuran was thus shown to be 3,4,6-trimethoxydibenzofuran-2,7-diol (9). The compound was not found in healthy sapwood and is probably a phytoalexin.