C-Nucleosides and related compounds. XII. The synthesis of the carbocyclic analogues of D, L-6-azapseudouridine, 2-thio-6-azapseu douridine, and pyrazofurin A. On the cyclization of semicarbazones of α-keto esters

Abstract

GEORGE JUST and SUNGGAK KIM. Can. J. Chem. 55, 427 (1977). The preparation of the title compounds is described. The cycli~ation of the syn-and antiisomers of semicarbazones, thiosemicarbazones, and carbomethoxymethyl hydrazones to azauracils, thioazauracils, and pyrazoles is described. The photochemical isomerization of the hydrazones has been carried out. Whereas both syn-and anti-isomers of the thiosemicarbazones and carbomethoxymethyl hydrazones cyclize, only the syrz-isomer of the semicarbazones can be converted to the corresponding azauracil.GEORGE JUST et SUNGGAK KIM. Can. J. Chem. 55, 427 (1977) On decrit la preparation des composes mentionnes dans le titre. On decrit la cyclisation des isomeres syn et anti des semicarbazones, des thiosemicarbazones et des carbomethoxymtthyles hydrazones en azauracils, thioazauracils et pyrazoles. On a effectut les isomCrisations photochimiques des hydrazones. Alors que les isomeres syn ainsi que anti des thiosemicarbazones et carbomethoxymCthyles hydrazones peuvent se cycliser, il n'y a que l'isomere syn des semicarbazones qui peut &tre transform6 en azauracil correspondant.[Traduit par le journal]In the course of the synthesis of the carbocyclic analogue of D,L-pyrazofurin A 17 (I), it was noted that the cyclization of the corresponding hydrazone 10 proceeded in low yield, and that the hydrazone consisted of a mixture of the synand anti-isomers. It occurred to us that perhaps only one isomer underwent cyclization.The cyclization behaviour of semicarbazones is also a somewhat capricious reaction. It has of pyruvic acid underwent a high yield cyclization resulting in the formation of 6. Replacement of the sulfur atom with an oxygen atom then allowed him to prepare 6-azathymine 4 (5). In contrast with the cyclization of semicarbazones of a-keto acids, the cyclization of thiosemicarbazones proceeds consistently in good yield.

A Convenient Protocol for Selective Cleavage of 2-Hydroxy Acid Amides. Application to Semisynthesis of the Cyclic Heptapeptide Aza HUN-7293

“…On the basis of simple model substrates two potential approaches were evaluated. Method A is founded on a report on the cyclization of the thiosemicarbazones of sodium pyruvic acid esters and subsequent ester cleavage. First, coupling of sodium pyruvate ( 2 ) and d , l -Val-OMe ( 3 ) in the presence of EDC afforded our model substrate N -(2-oxopropanoyl)leucine methyl ester ( 4 ).…”

First cobalt complexes with methyl pyruvate semi/thiosemicarbazone - synthesis, physico-chemical and structural characterization

“…These could be ascribed to ν(C=O) vibrations of COOMe-and CONH 2 -groups, respectively. 46 On the contrary, the spectrum of the Hmpt ligand in this region contains only one band of very high ________________________________________________________________________________________________________________________ Available on line at www.shd.org.rs/JSCS/ (CC) 2020 SCS.…”

Five‐Membered Heterocycles: 1,2‐Azoles. Part 1. Pyrazoles

“…Dieckmann cyclization of hydrazones 55 leads to 4-hydroxypyrazole-5-carboxylic acid derivatives 56 in moderate to good yields (Scheme 8.13) [101,102]. Trifluoroacetic anhydride-pyridine induced cyclization of hydrazones 57 affords 1-alkyl-4-trifluoromethylpyrazoles 58 [103].…”