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The compound CI8Hl8O5 isolated during the purification of curvularin is shown to be ap-dehydrocurvularin.THE culture filtrate of a species of Curvularia was reported in Part I to contain, in addition to curvularin (I), Cl,H,O5, a small quantity of a second compound, C,,H,,O,.Chemical tests on the latter showed it to be phenolic and to contain two hydroxyl groups while its i.r. absorption indicated the presence of two types of carbonyl group, one aliphatic and the other present in a hydroxybenzoyl system. Unlike curvularin it appeared not to be affected by oxygen in alkaline solution.We now report further work which establishes that the compound C,,HI8O5 has the structure (11). Its molecular formula and its origin suggested a close relationship to curvularin and this was established by its hydrogenation over Adams catalyst which gave curvularin quantitatively. The compound is therefore a dehydrocurvularin. Its U.V. absorption bears a general resemblance to that of curvularin but the weaker absorption bands are shifted to longer wavelengths. The absorption above 2600A is similar to that shown by 2-hydroxy-4-methoxycrotonophenone and by 2,4-dihydroxybenzo-phenone4 suggesting that the aryl carbonyl system of the compound is conjugated with the olefinic group. The i.r. absorption is compatible with this arrangement, the aryl carbonyl band at 1633 cm.-l resembling those shown by 2-hydroxy-4-methoxycrotonophenone (at 1647 cm.3) and by 2,4,3'-trihydroxybenzophenone (at 1642 cm.-l). In addition there are bands at 1298 and 973 cm.-l which are not shown by curvularin and which can be attributed to a conjugated trans-olefinic group. The two olefinic protons appear in the nuclear magnetic resonance (n.m.r.) spectrum as a complex multiplet centred at ca. 7 3.27, a value which also indicates that the double bond is conjugated with the carbonyl group.

Bowie and Muspave. 3945 749. Organoboron Compounds. Part V.* The Hydrolysis of Cyclic Phen y lboronates.

The mould metabolite, curvularin, has been shown to be a lactone (VI; Its biosynthesis involves the R = H) containing a twelve-membered ring. head-to-tail linkage of eight acetic acid units.PRELIMINARY work1s2 indicated the partial structure (I;a metabolite of a Curvularia species [F334 in the Nobel Division Collection (Imperial Chemical Industries Limited) ; Commonwealth Mycological Institute Cat. No. I.M.I. 52,9801. We present here evidence defining the structure and the biosynthetic units involved.Structure.-The structural work can be resolved into determination of the number of C-Me groups, definition of the unknown oxygen functions, and their location.The original assignment of 2 C-Me groups rested on the production of ca. 1.5 mols. of acetic acid on Kuhn-Roth oxidation. In our hands this oxidation gave 1.05 and 0.89 mol. in replicate determinations, indicating that curvularin may have only one C-Me group. We reached a decision in a novel way. The partial structure (I) suggested biosynthesis, a t least in part, from acetic acid units: in particular, formation of the acylresorcinol fragment could be envisaged as involving cyclisation of an intermediate of partial structure (11) containing a carbon chain formed by serial head-to-tail linkage of acetic acid units3 We found that the mould incorporated radioactivity from MeJ4C0,H into curvularin to the extent of ca. 4% and that the acetic acid produced by Kuhn-Roth oxidation contained approximately one-eighth of the total activity, all of it on the carboxyl group. We can therefore infer that the C,, metabolite is derived from eight acetic acid units very probably incorporated through a straight-chain precursor, a conclusion later supported by examination of other degradations set out below. It therefore contains one C-Me group which is presumably associated with the acetic acid unit a t one end of the chain. We believed that the presence of 2 C-Me groups would have implied a biosynthesis from eight acetic acid units (one of them decarboxylated), with the *

A number of new sec.-aminoboron dihalides has been prepared. The formation of cyclic dimers by these compounds is limited to the products obtained from pyrrolidine, piperidine, and morpholine. I n the other cases the steric effects of the substituents on the nitrogen atoms appear to prevent dimerisation.

The isolation of a new mould metabolic product, C,,H,,O,, from a species of Curmularia is described; a second compound, C16H1805, is also obtained in minor amount. The compound C,,H,,O,, for which the name " curvularin " is proposed, is shown by chemical and spectroscopic studies to contain two C-methyl groups, a dihydroxybenzoyl system, and an aliphatic carbonyl group.DURING an examination in 1953 of thc metabolic products of a number of moulds, C. T. Calam isolated a crystalline compound, in. p. 201-203", from the culture filtrate of a species of Curvularia. As there is no record of any previous investigation of the chemistry of the metabolic products of this genus a detailed examination of the compound was considered desirable. Through the courtesy of Dr. Calam, to whom I am glad to express my thanks, a culture of the mould and a specimen of the metabolic product were made available for further work. The mould was identified as a species of Cwvularia at the Commonwealth Mycological Institute at Kew ; it does not appear to have been described previously. Although when first isolated the mould produced spores, it later lost this capacity.The Curvularia was grown on a medium containing glucose, peptone, and mineral salts. Ether-extraction of the culture filtrate a€forded a solid (0*40--0.48 g. /l.) which on crystallisation gave in high yield a compound C16H2005, m. p. 206-206*5", [all8 -36.3", identical with that isolated by Calam. The name " curvularin " is proposed for this substance which has not been described previously. Curvularin contains two C-methyl groups and two active hydrogen atoms which are present in two hydroxyl groups. I t exhibits strong infrared absorption at 3356 cm.-l (hydroxyl) and forms a crystalline dibenzoate, C,,H,,O,, a crystalline di-9-chlorobenzoate, C30H,60,C12, and an amorphous diacetate, C2oH24O,, the spectra of which do not show this band. Curvularin possesses the properties of a phenol, giving a purple ferric reaction in aqueous ethanol, coupling with diazotised aniline in alkaline solution to give a red dye, and dissolving readily in aqueous alkali, from which it is precipitated unchanged by carbon dioxide. Treatment with ethereal diazomethane or dimethyl sulphate and potassium carbonate readily gives a dimethyl ether, C1,H,,05, showing that both hydroxyl groups are phenolic. The molecular formula of curvularin permits of the presence of only one benzene nucleus and hence both hydroxyl groups must be attached to this. The formulation of the compound as a dihydric phenol explains inter alia the sensitivity of its alkaline solutions to aerial oxidation. Curvularin fails to decolorise a solution of 2 : 6-dichlorophenolindophenol, showing that it does not contain a quinol grouping; this is confirmed by the blue colour developed in alkaline solution with 2 : 6-dichloroquinone chloroimide which indicates the presence of an unsubstituted position on the aromatic ring para to an hydroxyl group. The hydroxyl groups must therefore be ortho or meta to one another. Curvularin reacts with di...

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