6 - pyrid

Structurally unique, potent, and selective oxytocin antagonistic agents characterized by a cyclic hexapeptide structure have recently been isolated from the broth filtrate of a novel Streptomyces silvensis strain [434,435]. As shown in formula (106), these compounds contain two hexahydro-3-pyrid-azinecarboxylic acid moieties. A study has been made of their structural modifications (including oxidation of the reduced pyridazine nuclei) [436]. 

In the heterocyclic series, racemic 3-(fur-2-yl)alanine has been prepared from furfural using this approach. In addition, (3-(pyrid-3-yl)alanine, ° p-(quinol-3-yl)alanine, ° a p-(benzofuranyl)alanine derivative, 2-amino-3-(2,2 -bipyridi-nyl)propanoic acid, and some interesting derivatives of histidines—in particular 1-alkylhistidines with amphiphilic properties have all been synthesized using this methodology. The complete reaction sequence starting from an aldehyde and an A-acylamino acid derivative is shown in Scheme 7.150. 

The first asymmetric autocatalysis was attained with chiral pyridyl alkanols 49. When 3-pyrid-inecarbaldehyde 48 was reacted with dialkylzinc by using chiral pyridyl alkanol 49 (20 mol %) as asymmetric autocatalyst, enantio-enriched pyridyl alkanol 49 with the same structure and configuration as that of the catalyst was obtained [43]. Regarding the substituents (R) of pyridyl... 

Arylamino)-5//-pyrrolo[3,4-6]pyridinc-5,7(6//)-diones rearrange to 6-arylpyrido[2,3-(/]pyrid-azine-5,8(6/7,7//)-diones 4 by refluxing in a mixture of 25% hydrochloric acid and acetic acid.79... 

NE-kB Nuclear factor kappa-light-chain-enhancer of activated B cells NHANES National Health and Nutrition Examination Survey NNK 4-(N-methyl-N-nitrosamino)-1 -(3-pyridal)-1 -butanone... 

Benzoyl diloride added dropwise at -15° to 2-methylindole in pyridine, allowed to warm slowly to room temp., and stirring continued 3 days with passage of oxygen or oxygen-air 2-methyl-3-(pyrid-4-yl)indole. Y 67%. F. e. s. H. Deubel et al., B. 104, 705 (1971). 

Depending on the respective reaction partner, acetic acid esters can react either as C-H acidic compounds or as acylating agents. Both are illustrated by the self-condensation of ethyl [ 1 acetate in the presence of 0.5 equivalent of sodium ethoxide or triphenymethyl sodium to give ethyl [1,3- C2]acetoacetate (Claisen condensation). In the first case, however, because of the relatively low radiochemical yields (40-45%) obtained by this procedure, it is of minor importance for the preparation of labeled ethyl acetoacetate. The deprotonation of alkyl acetates with LiHMDS followed by acylation with unlabeled or labeled acyl halides to labeled give /3-keto esters is discussed in Section 6.4. Claisen condensation of alkyl [ CJacetates with esters lacking a-hydrogens (i.e. ethyl formate, diethyl oxalate, aromatic/heteroaromatic carboxylic acid esters) proceed unidirectionally and are valuable pathways in the synthesis of ethyl [ C]formyl acetate (521. diethyl [ C]-oxaloacetate (53) and ethyl 3-oxo-3-pyrid-3-yl[2- C]acetate (54). The last example... 

---