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• 952-92-1 1-Benzyl-1,4-dihydronicotinamide 

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High- and Low-Potential Flavin Mimics. 2. 3,7,10-Trimethyl-(1H,3H,5H,7H,9H,10H)-pyrimidopteridine-2,4,6,8-tetrone Dianion Reduction of Carbonyl, Nicotinamides, and Alkyl Disulfide Functional Groups

3,7,10-Trimethyl-(3H,7H,9H,10H)-pyrimidopteridine-2,4,6,8-tetrone (PPTox) and its conjugate base (PPTox-) undergo two-electron reduction to yield 3,7,10-trimethyl-(1H,3H,5H,7H,9H,10H)-pyrimidopteridine-2,4,6,8-tetrone (PPTH2) and its dianion (PPT2-) (Scheme I).The two-electron redox potential E0' is 150 mV more negative than that of the corresponding 3-methyllumiflavin (Flox)/1,5-dihydro-3-methyllumiflavin (FlH2 + FlH-) couple.Reductive alkylation of PPTH2 with acetaldehyde (Scheme II) provides the N5-ethyl derivative of PPTH2 (N5-EtPPTH2) which is an analogue of the well studied 1,5-dihydro-N5-ethyl-3-methyllumiflavin (N5-EtFlH).As in the instance of N5-EtFlH, N5-EtPPTH2 can undergo stepwise oxidation to the thermodynamically stable N5-EtPPT-. radical (analogue of N5-EtFl.) and hence to the two-electron oxidized species N5-EtPPTox (Scheme II).The pKa for the pseidobase formation via reaction of N5-EtPPTox with H2O (7.34) is compared to the similar pKa (4.00) for the reaction of N5-EtFlox+ with H2O.The species PPTox- (like Flox) is not reduced (H2O solvent) with NaCNBH3.However, reduction of a solution of PPTox- containing formaldehyde with NaCNBH3 yields N5-MePPTox and the radical N5-MePPT-. on admittance of O2.The mechanism (Scheme III) involves the initial formation of the N1-carbinolamine of PPTox- which when reduced is subject to reductive alkylation at N5, as in the case of reductive alkylation of PPTH2.The reaction of PPTH2 with formaldehyde has been studied in detail.The reaction resembles, in important details, that for the reaction of FlH2 with formaldehyde.An initial first-order burst in the formation of PPTox- is associated with the competitive reduction of formaldehyde by PPT2- and the formation of the N5-imine of PPT2- (eq 5; Scheme IV).The latter does not apparently revert readily to carbinolamine, due to its electronic stabilization (structures A, B, C, and D).The N5-imine of PPT2- is trapped in further reactions to produce compounds with more positive potentials than that for the PPTox-/PPTH2 couple (possible structures as E, F, etc.).The increase in the rate constant of specific acid catalyzed reduction of formaldehyde by PPT2- (k = 3.3x106 M-2 s-1) over the like constant with FlH- (k = 2.3x104 M-2 s-1) is related to the difference in the two-electron reduction potential for the two (148 mV) by the free energy relationship 67 mV/Δ log k.The predicted free energy relationship for a series of 1,5-dihydroflavins of varying potentials carrying out reduction of a substrate by two-electron transfer would be 60 mV/Δ log k.Thus, toward formaldehyde, PPT2- exhibits the reactivity of a low-potential FlH- molecule.The reaction of PPTH2T (=PPTH2 + PPT- + PPT2-) with m-hydroxybenzaldehyde was studied at pH 5.00 only.In preparative experiments, it was shown that m-hydroxybenzaldehyde was reduced to m-cresol and a trace of m-hydroxybenzyl ...

HOST-GUEST-TYPE ACID CATALYSTS DERIVED FROM CALIXARENE

Water-soluble calixarenes bearing both acidic protons and sulfonate groups were synthesized.They catalyzed a hydration reaction of 1-benzyl-1,4-dihydronicotinamide (BNAH) according to Michaelis-Menten kineticts and the rate constants were greater by 426-1220 fold than those for noncyclic analogues.Fluorescence data supported the complexation of BNAH with these water-soluble calixarenes.These findings indicate that calixarenes serve as a new starting material to design functionalized host molecules.

CALIXARENES. 23. THE COMPLEXATION AND CATALYTIC PROPERTIES OF WATER SOLUBLE CALIXARENES

A series of water-soluble calixarenes containing dialkylamino groups and carboxyl groups have been prepared by the p-quinonemethide route of functionalization.The formation of host-guest complexes between these calixarenes and nine aromatic hydrocarbons ranging in size from durene to decacyclene has been investigated, and a correlation between the dimensions of the hydrocarbons and the "lower rim" of the calixarene, containing the array of OH groups, has been made.A study of the effect on the acid-catalyzed hydration of N-benzyl-1,4-dihydronicotinamide by p-(carboxyethyl)calixarenes (n=4,5,6,7,8) has shown that the calixarene is more effective than either its larger or smaller analogs.