THE SITES OF REDUCTION AND BASE-CATALYZED HYDROGEN-EXCHANGE IN N¹-METHYLNICOTINAMIDE IODIDE¹

Nicotinamide Coenzymes

“…This observation implied the dissociation of protons t!rom that carbon atom, leaving a carbanion. Later, this dissociation was confirmed in nuclear magnetic resonance studies (27). It would therefore appear that the quaternary nitrogen in a pyridine ring can function like that in a thiazole ring (28) and stabilize the transient formation of a carbanion ~t the a-position.…”

Determination of the hydride transfer stereospecificity of nicotinamide adenine dinucleotide linked oxidoreductases by proton magnetic resonance

“…The retention of a proton at the pyridine 4 position in methods I and III could be quantitatively determined bycomparing the integration of its resonance to that of the resonance for the proton at the pyridine 6 position (see Figure 2a for the designation of the pyridine proton resonances). In this regard, one should not use the resonance of the proton at the pyridine 2 position as an integration standard, since this proton undergoes partial deuterium exchange with 2H20 during the formation of [4B-2H]NADH (San Pietro, 1955;Dubb et al, 1958).…”

Studies on the C–H/C–D Exchange in Imidazolium (Pilocarpinium) and in 2‐ and 4‐Hydroximinomethyl Pyridinium Compounds

“…A great number of observations on H-D exchange of carbon bound hydrogen in various five [1][2][3][4][5][6][7][8] and six [9][10][11][12][13][14][15][16] membered heteroaromatic rings has been reported, and ylid [2-6, 12, 17] or anionic [II, 13] intermediates have been proposed. The nature of these heterocyclic ylids which can be generated in pro tic solvents are of considerable chemical and biochemical interest [2,9]. In most cases the results have indicated that the H-D exchange takes place under controlled basic conditions such as aq.…”

“…In most cases the results have indicated that the H-D exchange takes place under controlled basic conditions such as aq. Na2C03 [9], CD 30D-CH30Na [16], D 20+NaOD [12], [13] or in D 20 alone with heating. The evidence supporting the formation of an ylid is the facile exchange of a proton bonded to an Sp2 carbon atom adjacent to a formally charged heteroatom [2][3][4][5][6]9].…”

“…Na2C03 [9], CD 30D-CH30Na [16], D 20+NaOD [12], [13] or in D 20 alone with heating. The evidence supporting the formation of an ylid is the facile exchange of a proton bonded to an Sp2 carbon atom adjacent to a formally charged heteroatom [2][3][4][5][6]9]. The same mechanism includes the case of free bases previously protonated by the solvent [3,7,12].…”