Synthesis and biological activities of condensed

Synthesis and Biological Activities of Condensed Heterocyclofn, m-a, b, or cJQuinazolines... 

Synthesis, set also Heterocyclic synthesis and biological activities of condensed heterocycloln.m-tj, b, or cjquinazolines. 52, I and reactions of l-azirines, 13, 45 of condensed l,2,4-triazolo[3,4-z)heterocycles, 49, 277 by ring-closure of o-substituted t-anilines, 14, 211... 

The domino process probably involves the chiral enamine intermediate 2-817 formed by reaction of ketone 2-813 with 2-815. With regard to the subsequent cy-doaddition step of 2-817 with the Knoevenagel condensation product 2-816, it is interesting to note that only a normal Diels-Alder process operates with the 1,3-bu-tadiene moiety in 2-817 and not a hetero-Diels-Alder reaction with the 1-oxa-l,3-butadiene moiety in 2-816. The formed spirocydic ketones 2-818/2-819 can be used in natural products synthesis and in medidnal chemistry [410]. They have also been used in the preparation of exotic amino adds these were used to modify the physical properties and biological activities of peptides, peptidomimetics, and proteins... 

The biological activities of condensed pyrimidine systems as diuretics, antitumor agents or as antagonists of constituents of nucleic acid and of folic-folinic acid family of vitamins prompted differents authors to study the synthesis of cyclic six membered acylureas such as pyrido[2,3-d] pyrimidinones (Ref. 266). 

Nosova E, Lipunova G, Charushin V (2007) Fluorine-containing derivatives of condensed quinolines and related systems synthesis and biological activity. In Kartsev V (ed) Selected methods for synthesis and modification of heterocycles. Quinolones chemistry tmd biological activity. ICSPF, Moscow... 

Among other condensed thiazole ring systems, imidazo[2,l-6]thiazoles (tetramisole is a member of this class), thiazolo-pyrimidines, and thiazolo-pyridines continue to attract the most interest. Attention is concentrated on synthesis and biological activity. Unexpectedly, dihydrothiazolo[3,2-a]pyridinium bromide is readily brominated when the pyridine ring has a 3-nitro-substituent but not when it has a 3-amino-substituent. 

Condensation of N -substituted hydroxylamines with aldehydes and ketones is widely used in the synthesis of various spin traps and biologically active nitrones (Fig. 2.5) (161-186). 

A measure of the interest in the biological activity of these dibenzyl-butyrolactone lignans is evinced in the recent spate of publications dealing with the total synthesis of the natural optically active products. Again, the Stobbe condensation pathway (Scheme 9) has been usefully exploited for this purpose. In a series of papers, resolution of the intermediate hemisuccinate esters (433 by chiral bases has been described (54), as has asymmetric hydrogenation (55), and the optically active lignan products synthesized in the usual way (42 - 44 45). 

In nature, the intramolecular condensation of a 1,3-dicarbonyl moiety with a keto group in polyketides is an important step in the biosynthesis of aromatic compounds. Biomimetic transformations of this type have been intensively investigated by Harris. (For a discussion, see Chapter 1.5, this volume.) In the following, the synthesis of some natural products and biologically active compounds using the Knoevenagel reaction will be described. 

In a large number of publications the use of 3-hydroxy-1,2,3-benzotriazin-4(3//)-one (4) as a condensation agent in peptide synthesis is described. Finally, the imidazo[4,5-r/]-l,2,3-triazines, e.g. 5, represent the 2-azapurine system. Therefore, in many papers, the biological activity of 2-azaadenine (6) or 2-azahypoxanthine (7), its ribose derivatives and its ribose phosphates were discussed. 

The unique structures and important biological activities of the streptovaricins have attracted considerable attention of synthetic chemists. There are several synthetic approaches to the streptovaricin ansa chains and also to the naphthoquinone nucleus. Several building blocks for the synthesis of the ansa chain of streptovaricin A (105) have been prepared by aldol condensations, [194] by ring-opening of epoxides [195] and by the strategy termed pyranosic homologation [196]. 

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