6 - pyrid structure

The determination of the structure of adenine hydrochloride (see Volume 2, Section IV,K, of article IV by Katritzky and Lagowski) is an example of extremely accurate X-ray crystallography whereby the positions of individual hydrogen atoms were located. An example of the deduction of structure from bond lengths between heavy atoms is provided by Penfold s investigation of pyrid-2-thione. ... 

Dipole moment data have provided valuable information for the study of the tautomerism of compounds such as isonicotinic acid, pyrid-4-one, and ethyl acetoacetate, However, this method must be used with discretion since it can lead to inconclusive results. Thus, the fact that 4-aminopyridine has a higher dipole moment than the algebraic sum of the dipole moments of pyridine and aniline was originally interpreted as proof that structure 54 exists with a strong contribution from 36, and it was stated that 55 w ould have a very low moment. Later, Angyal and AngyaF pointed out that the... 

Hoffman and Gronowitz - have applied this technique with marked success to the study of hydroxy-, amino-, and mercapto-thiophenes. Similarly, it has been shown that pyrid-4-one exists predominantly as such and that 4-hydroxypyridine 1-oxide is in equilibrium with comparable amounts of l-hydroxypyrid-4-one. - The method has also been used to investigate the structure of ions (see Section II,C, of article II by Katritzky and Lagowski). 

The foregoing conclusions are further supported by a refined X-ray analysis of pyrid-2-one, which indicated that the mobile hydrogen atom is attached to the nitrogen atom in the solid state and that individual molecules are bound into helices by N—H- -0 hydrogen bonds. An oxo structure is also indicated by the molar refractivity of pyrid-2-one. The dipole moment of 4-methoxypyridine is ca. 3.0 debyes in dioxane, whereas the values for pyrid-4-one and its 1-methyl derivative are much higher, ca. 6.0 debyes indicating the... 

The reaction of several substituted imidazo[4,5-c/]-, pyrazolo[3,4-r/]- and triazolo[4,5-zf]pyrid-azines 3 with ynamines, in competition with [4 + 2] cycloaddition, leads to [2 + 2] derivatives 4, which rearrange to l,2-diazocines5.7 8 The reaction seems to be sensitive to the substituents, as replacement of the electron-withdrawing group R on the pyridazine ring of the pyrazolo compound (A = N, B = CH) by chlorine completely inhibits both the [4 + 2] and [2 + 2] cycloaddition reactions. The X-ray structure of the imidazo derivative 5 (R = Ms, A = CH, B = N) reveals a tub conformation of the eight-membered ring. 

Other workers began to study the structure of gramicidin. Christensen and coworkers12 isolated crystalline tryptophane and leucine from a hydrolysate. They found no evidence for a fatty acid component and established that phenylalanine, proline and hydroxyproline were absent from a hydrolysate. These workers isolated alanine diox-pyridate from a hydrolysate and also established that gramicidin contained a compound with vicinal hydroxy and amino groups. They speculated that this compound might be serine or isoserine and proposed that gramicidin contains two tryptophane, 2 leucine, 2 or 3 alanine and 1 hydroxyamino residues or a multiple of this composition. 

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]. 

Alkylation of the silver salt of pyrid-2-ones usually gives exclusive O-alkylation, whereas alkylation of the sodium or potassium salt gives predominantly TV-alkylation, e.g. Scheme 98. However, the course of such reactions is strongly dependent on conditions. Not only is the nature of the metal salt important but also the structure of the halide, the substituents on the pyridone ring and the solvent used (770PP5,70JOC2517,67JOC4040). 

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... 

Related to the mechanism of the above structure is the ring-chain-ring isomerization of 3-(2-pyridyl)-[l, 2,3 triazolo 1,5-zz pyrid-7-yl derivatives (139) into 6- 11, 2,3]triazolo 1,5-a ]pyrid-3-yl ] -2-pyridyl derivatives (141) via a diazo compound 140 [139],... 

The Michael-type addition of maleic hydrazide to activated olefins has been investigated. Maleic hydrazide when treated with methyl acrylate, acrylonitrile, methyl vinyl ketone, and other activated olefins forms monoaddition products - for which the structure as A-substituted derivatives has been determined. The exclusive formation of monoaddition products is in contrast to the saturated cyclic succinhydrazide which can form mono- and diaddition products. Additions of the foregoing type are valid also for pyrid-azinones. Low yields of addition products have been obtained when adding dihydropyran or its thio analog and dihydrofuran to pyrid-azinones or pyridazinethiones. ... 

The potassium salt of the hexadentate tris[3- (4-tbutyl)-pyrid-2-yl -pyrazol-l-yl]hydroborate (TpBuPy) has been described together with the crystal structure of [La(N03)2(TpBuPy)].166... 

Methanol, JV-methyIumdazol-2-yldi pyrid-2-yl)-, 88 metal complexes, 89 Methionine metal complexes, 749 Methyleneamido complexes transition metal, 125,129 bonding, 127 reactions, 128 spectroscopy, 128 structures, 127,128 synthesis, 126... 

Several copper peroxo complexes containing trl5(pyrid-2-ylmethyl)amine or related tripodal ligands have been reported. In contrast to (63)-(66), these complexes are characterized by a R02 —> Cu charge transfer band at Amax = 332-380 nm ( max = 890—4,300 mol dm cm Table i) i35,205,207,22r the values of vq o = 831—881 cm shown by (69)—(73) (Scheme 7, Table 1) 135,205,207 j-g similar to those of the pyrazolylborate complexes, however. The single-crystal structure of (69) shows a... 

The non-natural pyrid[2,3-d] pyrimidine nucleoside (195) pairs preferentially with guanine and adenine in DNA but specifically recognises AT base pairs within the triple helix structure. It is thought that this sequence specificity may be caused by the ability of the nucleoside to adopt different tautomeric forms. 

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