Concavine, an unusual diterpenic alkaloid produced by the fungus Clitocybe concava

A novel alkaloid with an unprecedented ring system consisting of a dodecahydro-7-oxa-9a-aza-benzo[a]azulene ring (1), has been isolated from cultures of Clitocybe concava (Basidiomycetae). Its structure and relative stereochemistry were elucidated on the basis of spectroscopic data. Concavine presents a weak antibacterial activity.     

Studies on decarboxylation reactions. Part 6 . Kinetic study of decarboxylation of 5-amino-1,3,4-oxadiazole-2-carboxylic acid and its N-phenyl derivatives at high hydrochloric acid concentrations

The dissociation constants (K₁) of both acids 4a-c and esters 5a-c and the rate constants of the decarboxylation reaction of acids 4a-c have been measured at various high concentrations of hydrochloric acid (0.5-8.0 M range). The results obtained have enabled us to suggest the probable structure of the zwitterion which undergoes decarboxylation.     

1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

The resolution of (1α,5α,6α)‐6‐bromo‐6‐fluoro‐1‐phenylbicyclo[3.1.0]hexane (rac‐ 5) provided the enantiomerically pure precursors (?)‐ 5 and (+)‐ 5 of 1‐phenyl‐1,2‐cyclohexadiene. On treatment of (?)‐ 5 with methyllithium in the presence of 2,5‐dimethylfuran, the pure (?)‐enantiomer of the [4+2] cycloadduct of 2,5‐dimethylfuran onto 1‐phenyl‐1,2‐cyclohexadiene was obtained exclusively. From this result, it is concluded that pure (M)‐1‐phenyl‐1,2‐cyclohexadiene ((M)‐ 7 ) emerged from (?)‐ 5 and was enantiospecifically intercepted to give the product. In the case of indene as trap for (M)‐ 7 , the (?)‐ and the (+)‐enantiomer of the [2+2] cycloadduct were formed in the ratio of 95:5. Highly surprising, remarkable enantioselectivities were also observed, when (M)‐ 7 was trapped with styrene to furnish two diastereomeric [2+2] cycloadducts. Hence, the achiral conformation of the diradical conceivable as intermediate cannot play a decisive part. The enantioselective generation of (M)‐ and (P)‐ 7 by the β‐elimination route was tested as well. Accordingly, 1‐bromo‐2‐phenylcyclohexene was exposed to the potassium salt of (?)‐menthol in the presence of 2,5‐dimethylfuran, and the enantiomeric [4+2] cycloadducts of the latter onto (M)‐ and (P)‐ 7 were produced in the ratio of 55:45.     

Direct Amination of Naphthazarin,Juglone, and Some Derivatives

Mono‐ and diamino‐derivatives of naphthazarin, 2‐methoxynaphthazarin, juglone and their methylethers were prepared by reaction with ammonia. The structure of the products was established by NMR studies. Some compounds were tested for cytotoxic activity.     

Stereoselective Synthesis of Enantiopure 6-Fluoromethyl Furo[3,4-c]-isoxazolidines

The title compounds 7a-c are prepared through a totally regio-and stereo-selective intramolecular 1,3-dipolar cycloaddition of nitrones; a chiral and optically pure sulfinyl function acts as a removable primary source of stereocontrol.     

Tin-mediated synthesis of lyso-phospholipids

1-O-Acyl-sn-glycero-3-phosphocholine and 1-O-acyl-sn-glycero-3-phosphoric acid have been prepared selectively and with high yields from the corresponding diols, glycerophosphoryl choline and glycerol-3-phosphate. Starting from the diols, the activated tin ketals were prepared in 2-propanol by reaction with dialkyltin oxide. The intermediates were acylated in the same solvent with long-chain fatty acid chlorides, giving the corresponding 1-acyl-lyso-phospholipids in high yield and with complete regioselectivity. The catalytic nature of the tin-mediated acylation and the relevance of the solvent are discussed.     

A study of the conformation of some 3,3′-bithienyl and biselenienyl derivatives by measurements of twisting powers in nematic liquid crystals and of dipole moments

The conformation of chiral 2,2′-dinitro-3,3′-bithienyl-4,4′-dicarboxylic acid (Ia), its dimethylester (Ib), and analogous selenium derivatives Ic and Id was investigated by means of induced cholesteric mesophases. A parallel investigation on the diester (Ib) and on other model 3,3′-bithienyls was carried out with dipole moment measurements. The conclusions reached with the two independent methods for derivative Ib are in excellent agreement and indicate, if a single conformation is assumed, a preferred cisoid conformation with a dihedral angle somewhat smaller than 90°. Alternatively, if the existence of both cisoid and transoid conformations having supplementary dihedral angles is assumed, the data indicate a higher population for the cisoid form.     

Laser film thickness modulation and induced small pattern generation

This paper deals with a recently observed effect of laser light on the growth of thin films on a CdS substrate deposited on glass. The possible origins of the phenomenon are analyzed and the experimental apparatus used to observe it is described.     

13C-NMR. Analysis of Dihydrogranaticin Methyl Ester. A case of mixed biogenesis

The ¹³C-NMR. spectrum of dihydrogranaticin methyl ester has been completely analyzed. Feeding experiments of CH₃ ¹³COONa to a culture of Streptomyces olivaceus have shown that only a sixteen carbon moiety of the antibiotic granaticin is of polyketide origin, thus confirming the hypothesis of a mixed biogenesis for this natural substance.     

Acremines H-N, novel prenylated polyketide metabolites produced by a strain of Acremonium byssoides

Five novel metabolites, acremines H-N, have been isolated from malt extract-peptone-glucose agar cultures of a strain of Acremonium byssoides. Their structures and stereochemistry were elucidated using a combination of ¹³C and ¹H homo and heteronuclear 2D NMR experiments. Acremines H-N inhibited the germination of sporangia of Plasmopara viticola.