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Pyrimidine-fused ring systems

A few examples have appeared of the formation of 3-amino-substituted pyrazine- and quin-oxalinecarboxylic derivatives by nucleophilic decomposition of their pyrimidine-fused ring systems (pteridines and analogues) (see also Section 6.03.4.1) <86JHC843,87JHC1013,91JHC1485>. [Pg.270]

It is easily possible to continue to insert nitrogen atoms into fused ring systems and some important compounds belong to these groups. The purines are part of DNA and RNA and are treated in Chapter 49, but simple purines play an important part in our lives. Coffee and tea owe their stimulant properties to caffeine, a simple trimethyl purine derivative. It has an imidazole ling fused to a pyrimidine ring and is aromatic in spite of the two carbonyl groups. [Pg.1175]

Methods of this type are best considered as reactions of the fused ring-systems in question (see Chapter 4.15). The example illustrated in Scheme 91 is of potential interest in pharmacology (75T1363, cf. 74CPB1938). The conversion of the 1-aminoadenosine (192) into the imidazolyltriazole (193) amounts to triazole formation from an amidrazone intermediate and a formyl group derived from the pyrimidine moiety. [Pg.771]

Most of the examples that were reported to experience a translocation process of one of the heteroatom substituents with one of the heteroatoms of the ring belong to pyrimidines and their fused ring systems. [Pg.108]

One review of a synthetic nature covered new routes to pyridazino-fused ring systems <04SL1123>. In addition to this, there were two reviews focusing on specific medicinal applications of some diazines. One covered the design, synthesis and SAR of 5-[(l-substituted) alkyl (or vinyl)] pyrimidine nucleosides as potential inhibitors of herpes viruses <04MI2749>, and the other described 4-thiophenoxy-N-(3,4,5-trialkoxyphenyl)pyrimidine-2-amines as potent and selective inhibitors of the T-cell p561ck tyrosine kinase <04MI747>. [Pg.304]

Imidazole is the common name used for 1,3-diazole. This is a stable, aromatic ring system, with a Bird Unified Aromaticity Index (Ia) value of 79. Its resonance and tautomeric forms were discussed in Chapter 7 (section 7.1.8). This ring frequently appears in pharmaceuticals fused-ring systems are also common. Thus, the all-important purines are formed from fusion of imidazole to pyrimidines and are the subject of section 9.17. There is no general method for forming the imidazole ring such as the Paal, Knorr, and Hantzsch syntheses we have discussed for other cycles, so specific syntheses must be performed. [Pg.235]

The synthesis of thiazolo[4,5-d]pyrimidines has been successfully accomplished by various methods. 4-Amino-5-ethoxycarbonylthiazole derivative has been cyclized to thiazolo[4,5-d]pyrimidine by its reaction with phenyl isothiocyanate [87], Many 4-amino-5-carbamoylthiazole derivatives have been cyclized to the corresponding thiazolo[4,5-d]pyrimidines using triethyl orthoformate/acetic anhydride mixture [88-91], Moreover, 4-amino-5-cyano thiazoles have been used to prepare the same fused ring system via their reaction with triethyl orthoformate, followed by treatment of the intermediate with hydrogen sulfide, guanidine, amines, and isothiocyanates [92, 93], Other thiazolo[4,5-d]pyrimidines have been obtained from 4-amino-5-cyano, carbamoyl, or ethoxycarbonyl thiazoles via cyclization with acetic anhydride [94] or formic acid [95],... [Pg.349]

It is possible to prepare pyrimidines from other heteromonocyclic compounds by a variety of processes, or from fused heterobicyclic systems which already contain a pyrimidine ring by preferentially degrading the unwanted second ring. In the latter case, the bicyclic system may best be made from a pyrimidine in the first place, occasionally even from the self-same pyrimidine to which it reverts on degradation. Such syntheses may be of interest but are certainly not of any utility. [Pg.119]

The cleavage of fused pyrazines represents an important method of synthesis of substituted pyrazines, particularly pyrazinecarboxylic acids. Pyrazine-2,3-dicarboxylic acid is usually prepared by the permanganate oxidation of either quinoxalines or phenazines. The pyrazine ring resembles the pyridine ring in its stability rather than the other diazines, pyridazine and pyrimidine. Fused systems such as pteridines may easily be converted under either acidic or basic conditions into pyrazine derivatives (Scheme 75). [Pg.190]

Heterocyclic amines are compounds that contain one or more nitrogen atoms as part of a ring. Saturated heterocyclic amines usually have the same chemistry as their open-chain analogs, but unsaturated heterocycles such as pyrrole, imidazole, pyridine, and pyrimidine are aromatic. All four are unusually stable, and all undergo aromatic substitution on reaction with electrophiles. Pyrrole is nonbasic because its nitrogen lone-pair electrons are part of the aromatic it system. Fused-ring heterocycles such as quinoline, isoquinoline, indole, and purine are also commonly found in biological molecules. [Pg.958]


See other pages where Pyrimidine-fused ring systems is mentioned: [Pg.570]    [Pg.570]    [Pg.328]    [Pg.218]    [Pg.686]    [Pg.356]    [Pg.409]    [Pg.228]    [Pg.722]    [Pg.195]    [Pg.313]    [Pg.228]    [Pg.56]    [Pg.218]    [Pg.313]    [Pg.608]    [Pg.80]    [Pg.308]    [Pg.722]    [Pg.572]    [Pg.346]    [Pg.441]    [Pg.650]    [Pg.113]    [Pg.2]    [Pg.20]    [Pg.750]    [Pg.572]    [Pg.293]    [Pg.662]    [Pg.5]    [Pg.325]    [Pg.168]    [Pg.866]   
See also in sourсe #XX -- [ Pg.20 ]




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