It has been brought to our attention by Professor Ch. Tamm (University of Basel) that the name punctatin has been used previously1 for a group of homoisoflavanones isolated from Eucomis punctutu L'Herit. We therefore propose modifying the name of the fungal metabolites isolated from Poroniu punctutu described in the above two communications and related publications2J from punctatins to punctaporonins. Thus antibiotic M95464 becomes punctaporonin A, etc.

No abstract

No abstract

The carbon skeleton of the polyether antibiotic lC1139603 (1) is shown to consist of a polyketide chain, derived from seven acetate units and six propionate units, combined with a &-unit of unknown origin.

The isolation, structure elucidation, and some chemical transformations of the dimeric macrolide, thiobiscephalosporolide A, are reported.Recently a number of pentaketide fungal metabolites containing ten-membered lactone rings have been isolated. These include the diplodialides A--D ( l H 4 ) , ' obtained from Diplodia pinea, and the pyrenolides A-C (5)-(7) 4,5 which were isolated from Pyrenophora teres. A hexaketide twelve-membered lactone, recifeiolide (8) has been obtained from Cephalosporium recifei whilst cladospolide A (9)7 is a phytotoxic metabolite of Cludosporium fuluum. Because of their biological activity and synthetic challenge they pose, there is considerable interest in these compounds8 '' and the related phorocantholides,'6 which are produced by insects. In a preliminary communication ' ' we described a dimeric lactone, thiobiscephalosporolide A (lo), obtained from Cephalosporium uphidicola. In this paper we present our full evidence for the structure together with some related chemical transformations.Thiobiscephalosporolide A, C20H3008S (M' 430) (lo), showed i.r. absorptions at 3 500 cm (OH) and 1725 and 1705 cm-' (M). In its mass spectrum it showed the loss of two molecules of water (430+412-+394) and two molecules of carbon monoxide (412-+384+356) confirming the presence of hydroxy and carbonyl groups. The 'H n.m.r. spectrum (see Table 1) contained resonances attributable to two secondary methyl groups [IS 1.18 (6 H, d, J 7.2 Hz)], a secondary thioether [S 3.95 (2 H, m)], two secondary alcohols [S 4.7 (2 H, m)], and two secondary lactones [IS 5.02 (2 H, m)]. However the 13C n.m.r. spectrum ( Table 2) contained only ten signals (1 Me, 4 CH,, 3 CHX, 1 0.CO and 1 CO) suggesting that the molecule was a C dimer.Thiobiscephalosporolide A formed a diacetate, C,,H3,0 1 oS ( M + 514) (Il), and a bis(trimethylsily1) ether, and was oxidized to a diketone, C20H,60,S (M' 426) (12), with pyridinium dichromate. These compounds did not show a hydroxy absorption in their spectra and hence thiobiscephalosporolide A contains only two hydroxy groups. Reduction with Raney nickel gave a monomeric desthio compound, cephalosporolide A, CIoHl6O4 ( M + 200) (13). This compound showed i.r. absorptions at 3 400 (OH), 1 730 (O.CO), and 1 680 (CO) cm ', and 13C n.m.r. signals (Table 2) attributable to 1 Me, 5 CH,, 2 CHX, a CO, and a CO group, suggesting that thiobiscephalosporolide A consists of two monomeric cephalosporolide A units joined by a sulphur bridge.Extensive 'H n.m.r. spin decoupling studies at 360 MHz on thiobiscephalosporolide and its derivatives enabled several part structures to be deduced. Thus irradiation at 6 5.02 led to the collapse of the methyl group doublet (6 1.18) to a singlet and perturbed a four-proton multiplet at 6 2.0, suggesting the presence of the part structure CH,CH(O.CO)Me. Irradiation at 6 4.70 resulted in the collapse of the multiplet at 6 3.95 to a double doublet and the conversion of the signals at 6 2.80 and 2.60 into a geminally coupled AB doublet, J 16.5 Hz. Irradiation at 6 3.95 n...