Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1971"

Cyano-13-epicobalamin(neovitamin B 12 )and its relatives.

Abstract: An equilibration between cobinamide and neocobinamide with K≈ 1 occurs under highly acidic conditions. Similar equilibrations are reported with cobyric acid, other monocarboxylic acids, a dicarboxylic acid fraction, dehydrocobinamide, and with vitamin B12 itself. The last process gives neovitamin B12, which has been crystallised. Compounds of the neo-series resemble rather closely the analogous normal compounds, except in chiroptical properties.Methanolysis of vitamin B12 and of neocobinamide gives heptamethyl dicyanocobyrinate and heptamethyl dicyanoneocobyrinate, respectively, the mass spectra of which suggest that they are isomeric. This is confirmed by the X-ray analysis of neovitamin B12 which shows it to be cyano-13-epicobalamin. In relation to the naturally derived corrinoids known so far, the neo-compounds are thus epimeric at C-13.

Experiments on the synthesis of tetracycline. VI. Oxidation and reduction of potential ring A precursors

Abstract: The reduction of substituted orcinol derivatives to dihydroaromatic compounds [specifically 2,6-dimethoxy-4-methylcyclohexa-2,5-dienecarboxamide (V)] is described. Attempted application of this reduction to the 3-dimethylamino-derivative (VI; R1= NH2, R2= Me, R3= NMe2) was unsuccessful. As an alternative route, the addition of a nitrene to the double bond of an enol ether was studied.The oxidation of a number of orcinol derivatives to the corresponding hydroxy-quinones is described. Attempts to hydrate these quinones were unsuccessful.The formation of certain ortho-acyloxycyclohexadienones from phenols by use of lead tetra-acetate is described. For the preparation of the starting phenols, boron trichloride is a convenient demethylating agent. Our results indicate that this reagent, contrary to previous reports, may cause selective demethylation para to a carbonyl group in certain polyoxygenated benzenes.

Studies in mycological chemistry. 28. Isolation and structure of deoxypurpurogenone, a minor pigment of Penicillium purpurogenum Stoll.

Abstract: A minor pigment has been isolated from the mycelium of Penicillium purpurogenum Stoll. Analytical, spectroscopic, and degradative investigations have established its close relationship to the major pigment, purpurogenone, and it has been assigned structure (1; R1= R2= H)(deoxypurpurogenone).

Transformation of the steroidal sapogenin side chain. II. A new method for the preparation of 16-alkylated-pregn-16-en-20-ones.

Abstract: The addition of Grignard reagents to some sapogenoic acid derivatives occurred at position 16α. The methyl esters gave 16α,26,26-trialkylspirostans which, by enol acetylation, oxidation, and saponification gave the corresponding 16-alkylpregn-16-en-20-one. Direct oxidation afforded 16α-alkylbisnorcholanic 22 → 16β-lactones (γ-lactones). Sapogenoic acids gave 16α-alkyl-20-oxospirostans (δ-lactones) and the amides the corresponding δ-lactams. Base-catalysed autoxidation of the γ- and δ-lactones gave the corresponding 16-alkylpregn-16-en-20-one directly.

Experiments on the synthesis of tetracycline. II. The synthesis of potential ring A and ring C-ring D components.

Abstract: The preparation of 3,4-dihydro-2-phenylnaphtho[1,8-bc]furan-5-one and methyl 6-acetoxy-4-diacetoxymethyl-benzisoxazole-7-carboxylate, as precursors of the CD ring system and of ring A, respectively, is described. Their condensation to a tricyclic ACD compound and subsequent attempts to transform this into 4-de(dimethylamino)-4a, 12a-anhydrotetracycline are presented.

Steroid conjugates. IV. The influence of the cation in borohydride reduction of ketol sulphates.

Abstract: Acetal formation is preferred to reduction when pyridinium salts of 3-keto-steroid sulphates are treated with sodium borohydride in anhydrous methanol, whereas alkali-metal salts are reduced in the normal way. This difference is explained by the acidity of the pyridinium ion, which is sufficient to promote acetalisation of unhindered ketones. Significant variations occur in the ratio of the epimeric alcohols formed in the presence of added cations.

Addition reactions of heterocyclic compounds. Part LIV. Rotational isomerism of 6-aralkyl-5-oxidovinylphenanthridiniums: an investigation by variable temperature nuclear magnetic resonance spectroscopy

Abstract: 5-Oxidovinylphenanthridiniums with 6-aryl substituents exhibit cis–trans and rotational isomerism. The nature of the species involved has been elucidated by variable temperature n.m.r. spectroscopy and by observation of the properties of related compounds.