Lorenzo Camarda

Screening of the genus Cercospora for secondary metabolites

Abstract Screening of 61 species of Cercospora grown on a potato-agar medium showed the presence of the phytotoxin cercosporin in 24 of them, and of dothistromin in 8. Some strains of C. beticola produce a yellow phytotoxin (CBT). The new metabolites cercosporin esters, ligustrone A, B, C, taiwapyrone, 3-methoxy-2,5,7-trihydroxy-1,4-naphthaquinone, cis -4,6-dihydroxymellein and ( − )-11-acetyldehydrocurvularin were isolated besides the known cynodontin, ( − )-dehydrocurvularin, (+ )-mellein and cis -3 S ,4 S -4-hydroxymellein.

Metabolites of Cercospora. Taiwapyrone, an α-pyrone of unusual structure from Cercospora taiwanensis

Abstract (+)-Mellein ( 1 ), cis-3 S ,4 S -4-hydroxymellein ( 3 ), and taiwapyrone ( 4 ), a new α-pyrone, have been isolated from the mycelium of Cercospora taiwanensis , grown on potato-agar. The structure and absolute configuration of ( 3 ) and ( 4 ) have been elucidated.

Rosigenin, an unusual metabolite from mycosphaerella rosigena

Abstract A new metabolite, 3,6-dimethyl-4,10-dihydroxy-2-oxaspiro[4.5]dec-7-en-1,9-dione ( 1a ), was isolated from a strain of Mycosphaerella rosigena grown on potato-agar medium. The structure was determined on the basis of chemical and spectroscopic evidence and confirmed by X-ray analysis.

Mycochromone and mycoxanthone: Two new metabolites from Mycosphaerella rosigena☆

Abstract Two new metabolites, dimethyl 2-(2-ethenyl-5-hydroxy-4H-1-benzopyran-4-onyl-3)-malonate (mycochromone 1a ) and methyl 2-methoxy-8-hydroxy-9-oxo-9H-xanthene-1-carboxylate (mycoxanthone 6a ), have been isolated and identified from the mycelium of Mycosphaerella rosigena grown on potato-agar.

Secondary mould metabolites. Part 13. Fungal perylenequinones: phleichrome, isophleichrome, and their endoperoxides

The helix-shaped, fungal pigment phleichrome has been isomerized to isophleichrome. The axial chirality and absolute configuration of the side-chain carbons of both perylenequinones have been established. Photo-oxidation of both compounds occurs stereospecifically to give their endoperoxides, whose structure and stereochemistry results from a detailed analysis of their n.m.r. spectra.

Dothistromin and 2-epidothistromin from Cercospora smilacis

Abstract Examination of a strain of Cercospora smilacis Thum grown on potato-agar medium showed the presence of the known phytotoxin dothistromin together with the new 2-epidothistromin. Mutual conversion by epimerization at C-2 occurred during derivatization.

Secondary mould metabolites. Part 15. Structure elucidation of rubellins A and B, two novel anthraquinone metabolites from Mycosphaerella rubella

The structure of rubellins A (1) and B (2), two novel anthraquinone metabolites isolated from Mycosphaerella rubella, have been assigned by detailed analysis of their 1H and 13C n.m.r. spectra and chemical evidence. Their relative configuration and conformation were deduced from the observed 1H–{1H} nuclear Overhauser effects (n.O.e.s) and the value of 1H–1H coupling constants.

Secondary metabolites from Mycosphaerella ligulicola

Abstract (+)-Epoxydon, together with the new (+)-epoxydon monoacetate, 3-methylidene-6-methoxy-1,4-benzodioxan-2-one and 2-(2-hydroxy-5-methoxyphenoxy)-acrylic acid, has been isolated and identified from the mycelium of Mycosphaerella ligulicola grown on Sabouraud-maltose 4 %-agar.

Structures of the red sandalwood pigments santalins A and B

The red sandalwood (Pterocarpus santalinus) pigment santalin A has been identified as 6-(3,4-dihydroxybenzyl)-2,10-dihydroxy-5-(4-hydroxy-2-methoxyphenyl)-1,3-dimethoxybenzo[a]xanthen-9-one (2) on the basis of degradative and spectroscopic evidence. Santalin B (3) is the corresponding 6-(4-hydroxy-3-methoxybenzyl) derivative. N.m.r. data, particularly those obtained by use of the shift reagent Eu(dpm)3, have led to the assignment of a revised structure (24) to per-O-methylsantarubin. A common biogenetic scheme for santalins and santarubin is suggested.

Colouring matters of the West African red woods Pterocarpus osun and P. soyauxii. Structures of santarubins A and B

The red heartwood of the West African trees Pterocarpus osun and P. soyauxii contains the pigments santarubins A and B and the known santalin A. Santarubins A and B have been identified as 6-(2,4-dimethoxybenzyl)-2,10-di-hydroxy-5-(4-hydroxy-3-methoxyphenyl)-1,3-dimethoxybenzo[a]xanthen-9-one (2a) and the corresponding 5-(3,4-dihydroxyphenyl) derivative (2b), respectively, on the basis of degradative and spectroscopic evidence, particularly the n.m.r. spectrum of the O-trideuteriomethyl derivatives in the presence of a lanthanoid shift reagent.