2- pyridine, spectral analysis

A library of trifluoromethyl-substituted thieno[2,3- ]pyridines has been established <2000JC024>. Structures have been confirmed by a combination of H NMR and IR spectral analysis as well as single crystal X-ray diffraction analysis. 

Several modifications of protoheme are indicated in Fig. 16-5. To determine which type of heme exists in a particular protein, it is customary to split off the heme by treatment with acetone and hydrochloric acid and to convert it by addition of pyridine to the pyridine hemochrome for spectral analysis. By this means, protoheme was shown to occur in hemoglobin, myoglobin, cytochromes of the b and P450 types, and catalases and many peroxidases. Cytochromes a and a3 contain heme a, while one of the terminal oxidase... 

On treatment with acetic anhydride in pyridine, the yellow tetraketone (68), the yellow triketone (66), and the diketone (67) afforded monoacetyl, diacetyl, and triacetyl derivatives, respectively. All these derivatives contained a tertiary acetoxyl group. However, comparisons of 1H-NMR spectra of the parent ketones with those of the acetyl derivatives indicated that a rearrangement of the molecule or a major conformational change must have occurred. On the basis of extensive H-NMR spectral analysis, structure 69 was proposed for the diacetyl derivative which was derived from the triketone 66. Structure 69 was justified on the basis of conformational arguments. 

Dehydration of hetisine diacetate (126) with phosphorus oxychloride and pyridine followed by basic hydrolysis afforded a mixture of olefins 136 and 137, whose structures were analyzed by H-NMR spectroscopy. These olefins can only be derived from hetisine diacetate if its structure is 126, a fact requiring the structure of hetisinone to be 128. Furthermore, hetisinone is stable to bases, behavior that is consistent with the assigned structure but less likely for either of the alternative /J-ketoalcohols 134 and 135. When hetisinone was heated in D2O-CFI3OD containing sodium deuteroxide, a mixture of deuterated hetisinones was obtained. Mass spectral analysis revealed the presence of 14% d, 53% d2, 24% d3, and 6% dA species. These data further confirmed that hetisinone is correctly represented as 128. 

Formation of a dihydropyridine -adduct at the chain-end was shown by NMR and UV" spectral analysis. Anderson and collaborators proposed that the actual initiator would be adduct 34, formed by reaction of s-BnLi with pyridine (equation 40), which implies that the a-end-group of PMMA is a dihydropyridine group. This hypothesis was not experimentally confirmed. However, in the specific case of the e-caprolactone (3, n = 4) polymerization initiated by the BnLi/pyridine addnct, no characteristic NMR signal of dihydropyridine could be detected. The polymerization mechanism was therefore revised, based on the alkyllithium as the actual initiator and the establishment of an equilibrium between an active uncomplexed enolate (35) and a dormant cr-complex (36) as the basis for polymerization control (equation 41)" . 

The molecular formula was established as C13H20N4O7S, and was supported by the H and 13C NMR spectra (26). The structure of the highly water-soluble compound was deduced through spectral analysis. Amide (1650 cm-1) and sulfonyl (1345 and 1165 cm1) groups were observed in the IR spectrum. An olefinic proton (7.39 ppm) and an JV-methyl group were observed in the NMR spectrum, together with a pair of exchangeable methylene protons (4.29 and 4.82 ppm). Methylation afforded a methyl ester, which permitted solubility in pyridine and clarification of some of the NMR resonances. The structure of altemicidin as 78 was deduced... 

Interest in alkaloids of the nicotine group appears to be on the increase. A review has appeared covering tobacco-specific nitrosamines, which may be causative factors in tobacco-related cancers. The solution conformation, and proton, deuterium, carbon-13, and nitrogen-15 n.m.r. spectra of nicotine and its 2- and 4-isomers, have been studied. A new synthesis of nornicotine and nicotine has been described, and a quantitative carbon-13 n.m.r. spectral analysis of nicotine that is labelled at positions 1, 2, and 3 with carbon-13 been presented. The synthesis and mass spectrometry of several structurally related nicotinoids have been reported. Nicotine is dehydrogenated on irradiation in benzene solution in the presence of benzophenone to l -methyl-2 -(3-pyri-dyl)pyrrole. ° Nornicotine has been synthesized in four steps from 3-bromo-pyridine and N-3-butenyl-phthalimide, using a palladium-catalysed vinylic... 

Acetylation is one of the most frequently used derivatization techniques in the mass spectral analysis of peptides. Reaction with freshly distilled acetic anhydride in methanol [27] results in acetylation of a-amino functionalities within one minute. Acetylation at other less reactive sites may be accelerated by the addition of a small amount of base, such as NaHC03 or triethylamine [28], Peptide hydroxyl and amino groups can be acety-lated by exposure to a 1 1 mixture of acetic anhydride/ pyridine for about 40 minutes. The net result of the reaction is a positive shift of 42 daltons for each acetyl group addition. The failure of an acetylation reaction in a peptide analysis may be diagnostic of a blocked N-terminus. 

Acetylation is also useful in the negative-ion mode. Peter-Katalinic et al. [33] have reported the advantages of peracetylation on the FAB target in the analysis of sulfated phlorotannins. In this study, micro scale peracetylation of hydroxy groups on aromatic carbons was performed using the direct addition of 2/acetic anhydride to the analyte. Derivatization on the FAB probe tip facilitates rapid mass spectral analysis and subsequently minimizes the time available for the decomposition of an unstable derivative. 

The mass spectral behavior of several nuclear and extranuclear nitroquinoxalines has been investigated in some detail.290,763 The X-ray analysis of 5-nitro-2,3-bis(pyridin-2-yl)quinoxaline1115 and its bisperchlorate salt1113 have been reported. Reduction to quinoxalinamines is the main transformation of nitroquinoxalines, but they also undergo useful displacement reactions. 

As reported in <1996GHEC-II(7)283>, no specific study on the mass spectra of these classes of compounds has been reported, although this analytical method has only been used as a tool for structure elucidation or reference without critical analysis. Some examples are reported in <1996GHEC-II(7)283>. Further information on the MS of heterocycles can be found in <2001MI1>. The mass spectral data for imidazopyridines, pyrazolo[3,4- ]pyridines, oxazolo-pyridines, ioxazolopyridines, isothiazolopyridines, 377-1,2-dithiolo[3,4- ]pyridines, and l,3-dithiolo[4,5- ]pyridines were reported in <1996GHEG-II(7)283>, but there have been no further reports in this area. 

Treatment of aromatic carboxaldehyde (diaminomethylene)hydrazones (105) with hot acetic anhydride or benzoyl chloride affords l,4-diacyl-3-acylamino-5-ary 1-4,5-dihydro- 1H-1,2,4-traizoles (106) in 75-95% yields. In contrast, when the 4-pyridine analog of 105 was employed, the unusual hemianimal triazole derivative (107) was obtained. The structures of the novel compounds were determined by spectral methods and in several cases by x-ray structural analysis. Mechanistic considerations are discussed [95M733]. The oxazole-1,2,4-triazole (108) was prepared by cyclization of the corresponding oxazolecarbonyl-thiosemicarbazide with bicarbonate, alkylation at the sulfur and oxidation to the sulfoxide with MCPBA [95JHC1235]. 

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