Two new diphenyl ethers, 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxybenzoic acid (micareic acid) (13), 4-(2-carboxy-3-heptyl-5-methoxyphenoxy)-2-heptyl-6-hydroxy-3-methoxybenzoic acid (methoxymicareic acid) (27) and a new depside, 4-(2-heptyl-6-hydroxy-4-methoxybenzoyloxy)- 2-heptyl-6-hydroxybenzoic acid (prasinic acid) (34) have been detected in chemical races of the lichen Micarea prasina Fr. and isolated and characterized as the corresponding methyl esters. The structure of the latter compounds has been confirmed by total synthesis. The key steps in the synthesis of the diphenyl ethers (14), (26) involved Ullmann-like condensation between the 3-chloro 2-enone (17) and the phenols (11), (31), and subsequent aromatization of the enol ethers (23) and (32). A biomimetic-type synthesis of methyl micareate (48) has also been achieved by treatment of the depside (33) with sodium hydride in dimethylformamide.

The corynetoxins, toxic metabolities of Corynebacterium rathayi formed in galled seed-heads of infected annual ryegrass, Lolium rigidum, are shown to be new members of the tunicamycin group of antibiotics. They consist of N-acetylglucosaminyl-tunicaminyl-uracil in amide linkage with fatty acids which differ in certain respects from those present in the tunicamycins. The corynetoxin acids are of slightly longer chain length, C15-C19, occur in a β-hydroxy as well as saturated and α,β-un-saturated series, and have anteiso, iso and normal chain terminations. β-Hydroxy acids have not been observed previously in the tunicamycin group and anteiso chains were reported only recently in the streptovirudin subgroup. Stereochemical identity of the C11-aminosugar in the corynetoxins with the tunicamine part of the tunicamycins is demonstrated by formation of a common hydrolysis product, di(N-trifluoro- acetyl)glucosaminyl-tunicaminyl-uracil. Analysis of the carbon-13 and proton n.m.r. spectra of the main components, corynetoxins H17a and U17a, confirms the stereochemistry proposed for tunicamine except that the glycosidic linkages are changed to α-galactosamine, β-glucosamine.

The organic extract of Plocamium cruciferum gave a complex mixture of fatty acid methyl esters (26%), the tribromotrichloroalkene (12), (7 %), n-heptadecane (O.4%), phytol(12 %) and the unusual hydroxy bisnor-monoterpene (15) (43 %). The absolute stereochemistry of the polyhalogenated alkene (12) was established by X-ray crystallography.The Rhodophyta are well established as a prime source of halogenated organic compound^,^ some of which exhibit interesting pharmacological One genus, Plocamium, has been particularly well studied by a number of g r o~p s .~-'~ Consequently many polyhalogenated monoterpenes representing four major acyclic, e.g. (1)-(4), and two monocyclic families, e.g. (5) and (6), have been identified. A feature of this genus has been the relative dearth of oxygenated monoterpenes.As part of a general survey of New Zealand algae for biological activity, the organic extract from Plocamium cruciferum was screened%ith positive results.A bulk sample of Plocamium cruciferum was collected subtidally from Barney's Rock, Rosy Morn, and yielded an organic extract as a mobile green oil (5.4% of * Disc bioassays were carried out with the following microorganisms : Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Aspevgillus niger, Sacchavomyces cevevisiae.

Theoretical considerations indicate that the electron distribution in 3,4,-dimethylenecyclobutene is non-uniform and a dipole moment of 0.71 D has been predicted by inclusion of non-neighbour core resonance integrals. Preliminary studies of the microwave spectrum of this compound provide a dipole moment of 0.618 � 0.011 D. The term "pseudo-alternant" is proposed to describe this phenomenon. In the present paper additional physical and chemical properties of 3,4,-dimethylene- cyclobutene are described. The observed low-field proton chemical shifts for 3,4-dimethylenecyclobutene are not accounted for using a ring current model and a small calculated paramagnetic current indicates properties usually associated with H�ckel 4n-hydrocarbons. A local anisotropy model provides a better account of the observed shift. The carbon-13- proton satellite spectrum of 3,4-dimethylenecyclobutene indicates similarities in the geometry of the four-membered ring to that in cyclobutene. In addition, infrared and ultraviolet spectra support the conclusion that this hydrocarbon be regarded as a cross-conjugated diene. A detailed discussion of the products arising from the bromination of 3,4-dimethylenecyclobutene under a variety of conditions indicates consecutive 1,4-addition of bromine across the four-membered ring, a property which has been associated with cross-conjugation. Hydrogenolysis, chlorination, iodination, and attempted Diels-Alder addition reactions are also described. 3,4-Dimethylenecyclobutene was prepared by the thermal rearrangement of hexa-1,5-diyne. The mechanisms of thermal and photolytic rearrangement of hexa-1,5-diyne are discussed using Woodward-Hoffmann postulates. 1,2-Dideutero-,1-ethyl-, and 1-n-propyl-3,4-dimethylenecyclobutene were also prepared by the thermal rearrangement of the corresponding diyne. In addition, the thermal rearrangement of hexa-1,5-diyne over the temperature range 290-700� to give variable quantities of 3,4-dimethylenecyclobutene, fulvene, and benzene is described. 3,4- Dimethylenecyclobutene is thermally rearranged to benzene at 680�.

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