Pyridine 1-oxide 3- hydroxy-, methylation

Methyl-3-[N-(l-phenyl-ethyl)-hydroxyamino]- -methylester E16a, 127 (R-NH-OH + En) Pyridin 3-(Dimethoxy-methyl)-4-(fnmy-3-hydroxy-cyclopentyl)-E7b/2, 483 C-[CH(OR)2]-1,2,4-triazin + 3-OH —1-(CO — CH3) — cyclopentan Pyridin-l-oxid 4-Ethoxy-2-(l-hydroxy-cyclohexyl)- E19d. 605 (H - Li/ -(- Keton) Pymolo l,2-a azepin 6-Ethenyl-5-methoxycarbonyl-3-oxo-(5R, 6S, 9aR )-octa-hy dro-E21b, 1974 l-[CH(OH) —... 

It was originally postulated that the methyl groups at C-4 were removed as COj -a suggestion that has proved to be correct. These groups are hydroxylated by a mixed-function oxidase which is NAD(P)H and Oj dependent. First, the 4a-methyl is attacked, yielding the 4 -hydroxymethyl-4 -methyl sterol. This reaction is catalyzed by a methyl sterol oxidase which has been solubilized and partially purified in Gaylor s laboratory [108]. The same enzyme preparation will, with reduced pyridine nucleotide and dioxygen, oxidize the C-30 carbon to a carboxylic acid. The 4a-methyl-4/8-hydroxymethyl-5a-cholestan-3j8-ol is not a substrate for sterol biosynthesis while its epimer is [5]. The detailed mechanisms for the enzymatic removal of C-30 and C-31 are not fully understood. The initial reaction yields a 4a-hydroxy-methyl sterol by inference however, neither the isolation nor the enzymatic formation of a 4a-hydroxymethyl sterol has been demonstrated in animal tissues. This may well result from the fact that the hydroxylation reaction is the slow step in the demethylation process [5]. 

An interesting variant on this scheme to form alkylpyridinecarboxylic acids by nitric acid oxidation has been described by Czech workers starting with 2,4- or 2,6-lutidine these bases are condensed with formaldehyde to yield unsymmetrical j3-(hydroxyethyl)methylpyridines. Nitric acid oxidation now occurs preferentially at the hydroxylated side chain yielding the corresponding methylpicolinic acids. Thus, 2,4-lutidine (X-60) is converted to a separable mixture of 4-(/3-hydroxyethyl)-2-methylpyridine (X-61), 4-[tris(hydroxy-methyl)methyl]-2-methylpyridine (X-62), and 2-( -hydtoxymethyl)4-methyl-pyridine (X-63). Nitric acid oxidation yields 2-methylpyridine-4-carboxylic acid (X-64) from X-61 and X-62, and 4-methylpyridine-2-carboxylic acid (X-65) from X-63. A similar reaction sequence carried out with 2,6-lutidine (X-66) affords ultimately 6-methylpyridine-2-carboxylic acid (X-67). 

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

Osmium Tetroxide Oxidation of a A -Cyanopregnene 20-Cyano-21-hydroxy-5j5-pregn-17(20)-ene-3,l l-dione21-methyl ether (8 g) isdissolved in 100 ml of benzene and 8 ml of pyridine. After the addition of 9.6 g of osmium tetroxide, the reaction mixture is stoppered and allowed to stand at room temperature for 5 days. The mixture is stirred for 24 hr with 160 ml of chloroform, 200 ml of methanol and 280 ml of an aqueous solution... 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

Alkyl-1,4-dihydropyridines on reaction with peracids undergo either extensive decomposition or biomimetic oxidation to A-alkylpyridinum salts (98JOC10001). However, A-methoxycarbonyl derivatives of 1,4- and 1,2-dihydro-pyridines (74) and (8a) react with m-CPBA to give the methyl tmns-2- 2>-chlorobenzoyloxy)-3-hydroxy-1,2,3,4-tetrahydropyridine-l-carboxylate (75) and methyl rran.s-2-(3-chlorobenzoyloxy)-3-hydroxy-l,2,3,6-tetrahydropyridine-l-carboxylate (76) in 65% and 66% yield, respectively (nonbiomimetic oxidation). The reaction is related to the interaction of peracids with enol ethers and involves the initial formation of an aminoepoxide, which is opened in situ by m-chlorobenzoic acid regio- and stereoselectively (57JA3234, 93JA7593). 

The five-coordinate complexes Ir(CO)(PPh3)2L, where HL = /3-diketone, A-benzoyl-A-phenyl-hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone, 2-hydroxy-8-methoxybenzophenone, were prepared from [Ir(CO)(PPh3)2Cl].632 The resulting compounds all underwent oxidative addition reactions with Br2. Reaction of [(cod)2IrCl]2 with N-substituted 3-hydroxy-2-methyl-4-pyridine gives the bichelated complex (389). 33... 

G. Pilcher, W. E. Acree Jr., J. R. Powell. Enthalpies of Combustion of the Pyridine N-oxide Derivatives 4-Methyl-, 3-Cyano-, 4-Cyano-, 3-Hydroxy-, 2-Carboxy-, 4-Carboxy-, and 3-Methyl-4-Nitro, and of the Pyridine Derivatives 2-Carboxy- and 4-Carboxy-. The Dissociation Enthalpies of the N-O Bonds. J. Chem. Thermodynamics 1998, 30, 869-878. (b) M. D. M. C. Ribeiro da Silva, personal communication. 

Very interesting results concerning the cytotoxicity of alkaloids isolated from the flowers of ornamental legume plant Senna spectabilis have been noted by Sriphong et al. . N,0-diacetylcassine, 3(f )-benzoyloxy-2(f )-methyl-6(f )-(lh-oxododecyl)-piperidine and 5-hydroxy-2-methyl-6-(lh-oxododecyl)-pyridine V-oxide exhibited cytotoxicity against KB cell lines. 

Pyridine jV-Methyl- pyridinium 2-Pyridone 3-Hydroxy-pyridine 4-Pyridone Pyridine jV-oxide Unknown(s)... 

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