Pyridine tetramic acid

Tetrahydropyrrolo[4,3-. ]pyridines can be synthesized from 5,5-dimethyltetramic acid, 84, in a sequence of steps that begins with aryl aldehydes to generate arylmethylene-substituted tetramic acids. A Michael reaction with methyl acetoacetate followed by treatment with ammonium acetate yields the tetrahydropyrrolopyridine derivatives (Scheme 20) <2005H(65)377>. A similar reaction can be carried out with aroyl-substituted butenolides to give substituted furopyridine derivatives. 

Tetramic acid 2b with ethyl chloroformate in the presence of pyridine give, via (V-ethoxycarbonylpyridinium cation, compound 73 (Section... 

Some examples of 0-D assemblies, Scheme 2.5.14, in co-crystals include hetero-meric carboxylic acid carboxylic acid dimers (1 1) [87], pyridine carboxylic acid dimers (1 1) [88], 2-aminopyrimidine carboxylic acid trimers (1 2) [89], pyridine di-hydroxybenzene trimers (2 1) [90], bipyridinexarboxylic acid trimers (1 2) [73], 2-aminopyrimidine carboxylic acid tetramers (2 2) [89, 91], bipyridine resorcinol tetramers (2 2) [74], 3,5-dinitrobenzoic acid nicotinic acid tetramers (2 2) [92], isonicotinamidexarboxylic acid tetramers (2 2) [93], 2-pyridone carboxylic acids pentamers (4 1) [94], melamine thymine tetramers (1 3) [95], melamine barbital hexamers (3 3) [96] and tripenylphosphine oxide with a variety of hydrogen-bond donors (1 1) [62, 97, 98]. 

Siliquariaspongia°, Theonella Macrolactones, atypical sterols, linear and cyclic peptides, cyclic depsipeptides, nitrogen-containing sesquiterpenes, pyridine derivatives, acetylenic derivatives, phosphorus derivatives analogues of calyculin, tetramic acid glycosides... 

Propylene Tetramer Propylene Tetramer Propylene Trimer Propyleneimine, Inhibited Propylethylene N-Propyl Mercaptan N-N-Propyl-L-Propanamine Prussic Acid Pseudohexyl Alcohol Pyrazine Hexahydride Pyridine Pyrocatechin Pyrocatechinic Acid Pyrocatechol Pyrocatechuic Acid Pyrofax... 

Bipyridine is bidentate it has two Lewis basic sites that can coordinate a cation or other Lewis acid. 14-Ane-4 is tetradentate, by virtue of the four Lewis basic electron pairs on the nitrogen atoms. The acetone-furan cyclic tetramer is also tetradentate but the Lewis basic donors in this case are oxygen atoms. The pyridocrown shown on the right-hand side of Figure 1 is hexadentate by virtue of one nitrogen and five oxygen atoms. All four of these structures are heterocycles. Bipyridine is actually two pyridine heterocycles that are linked. The furan-acetone tetramer and crown are both true heteromacrocycles but both contain heterocyclic units within them. These are sometimes called subcyclic units. 

The anhydrotrimer of 2-aminobenzaldehyde, formed from the monomer on standing, or more quickly by the action of dilute acid,15 has proved to have structure 5a.13,16 The anhydro tetramer (5b)13,16 is obtained when the monomer is dissolved in 5 N hydrochloric acid and the precipitated red anhydro tetramer dihydrochloride,15 for which structure 6 has been proposed,13 is made basic with aqueous pyridine. At low concentrations (e.g., 10-5 M), equilibrium favors depolymerization to the monomer, but at higher concentrations (e.g., 10-2 M), 5a and 6 are formed in proportions depending on the strength of acid. The reaction mechanism for the formation of these oligomers has been discussed.13 The trimer (5a) and the tetramer (5b) consist of three tightly bound tetrahydroquinazoline rings and 6 has a macrocyclic structure. It is... 

Other donor molecules react with phosphonitrilic compounds. Dioxane is said to facilitate the depolymerization of the high polymer (63) and of the phenyl derivatives (13). Acetone forms complexes with the amino acid derivatives of the tetramer (see p. 128 in ref. 3). It is possible that ether acts as a catalyst for the hydrolysis of the trimeric chloride. The effect of these solvents is subtle, since the solubilities of the trimeric chloride in ether, in pyridine, and in dioxane show no sign of any specific chemical interaction. 

Lactate dehydrogenase is a pyridine nucleotide oxidoreductase, a tetramer of 140 kD molecular weight, which has been extensively investigated (Bloxham et al., 1975 Eventoff et al., 1977). It catalyses the reversible oxidation of L-lactate to pyruvate using NAD+ as a coenzyme. The reaction scheme with a view of the active site with bound substrate and essential amino-acid side chains are depicted in Equation (3) and in Figure 17. The probable reaction mechanism, involving proton and hydride transfers,... 

Fig. 3 Class A SPs. 1 Ureidopyrimidone-based linear chains2 porphyria-based linear chains I folic acid tetramers columnar stacks 4 actin double-helical chains5 helicene helical chains6 C3-symmetrical molecules forming helical columnar stacks . 7 uracyl or pyridine-terminated anthracene forming linear chains 8 surfactant micelles linear polymers 9 2,3,6,7,10,1 l-hexa(l,4,7-trioxoacetyltriphenylene) columnar stacks. ...

Shinoda et al. reported a similar cychzation reaction with 3-bromomethyl-pyridine to give cyclic pyridinium tetramer 26 (Fig. 10) [55]. The protons of the cyclic tetramer had acidic nature, and were rapidly deuterated in D2O so-... 

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