The Yellow Toxins Produced by Cercospora Beticola. V. Structure of Beticolins 2 and 4

摘要

Several toxins were isolated from a mycelial extract of a Cercospora beticola strain. Two were obtained as monocrystals. They are isomorphous and represent the leading xanthraquinones, a new class of natural toxins. Beticolin 2 [8R-(8α, 14aα, 14β,17aα)]-methyl 16-chloro-2',5',6',9,11,14-hexahydroxy-(19-methyl-8,17a-oxirano)-1 ,7,8,12,13,14a, 17a-octahydro-9H, 17H-nsph-tho[2',3': 1,2]cyclohepta[5,6-c]xanthene-14a-acetate: C31 -H23ClO13, Mr = 638.97, orthorhombic, P212121, a = 20.230 (6), b=18.921(5), c = 8.205 (3) A, V= 3140.6 A3, Z = 4, Dx = 1.352 g cm-3,λ(Cu Kα) = 1.5418 A, μ= 15.46 cm-1, F (000) =1320, T=293K, structure solved by direct methods, R = 0.062 for 2480 observed reflections. Beticolin 4 [8R-(8α, 14aα, 14β,17aα)]-methyl 16-chloro-2', 5', 6', 9,11,14-hexahydroxy-(19-hydroxyme-thyl-8,17a-oxirano)-1,7,8,12,13,14a-octahydro-9H,17H-naphtho[2',3':1,2]cyclohepta[5,6-c]xanthene-14a-acetate: C31H23ClO14, Mr= 654.97, orthorhombic, P212121,a=20.585 (5), b = 18.721 (4), c = 8.206 (3) A, V = 3162.3 A3, Z = 4, Cx= 1.375 g cm-3, λ(CnKaα) = 1.5418 A, μ= 15.71cm-1, F(000) =1352, T = 293K, structure solved by iso morphous replacement, R = 0.09 for 1124 observed reflections. Biogenetic pathways relating beticolins to other subclasses of fungal metabolites (cebetins and xanthoquinodins) are detailed.