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The present study establishes relationships between structure and reactivity for the pyrroloquinoline and phenanthroline quinones. The electrochemical reductions of 1,7-and 1,10-phenanthroline-5,6-quinones, like other quinones, are reversible and occur by 2e-transfer in a single step in aqueous solution and by two le-transfer steps in aprotic media. The electron-withdrawing pyridine moieties both increase their potentials and stabilize their aprotic semiquinones. The electrochemistry of the cofactor methoxatin and its trimethylester derivative is similar to the phenanthroline quinones in aqueous solution. However, the electrochemical reductions ofmethoxatin and its triester in aprotic solutions are characterized by at least three potentials, each accounting for less than le-. This has been explained by the proposal of semiquinone complexing with itself and with quinone. Despite an electron-donating pyrrole moiety, methoxatin and its trimethylester have relatively high potentials in aprotic solution. This is presumably due to stabilization of radical anions by the aforementioned complexing or by delocalization with carboxylic acid and ester groups. The reduction potential of methoxatin, in both aqueous and aprotic solvent, suggests that oxidation of methanol should be a thermodynamically favorable process. No evidence for an electrochemically reduced state lower than the quinol was found for any ofthe compounds. Chemical reactivity is influenced by the orientation of the pyridine nitrogen. The two quinones with a pyridine nitrogen peri to a quinone carbonyl add and oxidize nucleophiles most readily.Methoxatin (compound Ia) plays the role ofcoenzyme in various bacterial NAD(P)-independent alcohol, glucose, aldehyde, and perhaps methylamine dehydrogenases (1-5). Its structure, totally novel for a coenzyme, has been identified (1, 2) and its synthesis has been accomplished (6, 7), but little about its chemistry has been established. It has been proposed (8) MATERIALS AND METHODS Synthesis and Properties of I, HI, and Ill. Quinones Ia and lb were totally synthesized by an existing method (6). Dione III was obtained from Alfa-Ventron. 1,7-Phenanthroline dione (II) was synthesized as follows. A solution of 1,7-phenanthroline (Alfa-Ventron, 2.7 g) in fuming H2SO4 (18 ml) and fuming HNO3 (9 ml) was heated at 180°C for 3.5 hr, poured onto crushed ice, and brought to pH 6 with water saturated with Na2CO3. The collected precipitate was washed with water and recrystallized from methanol (MeOH) to yield pure, orange-brown HI (0.78 g): mp 258-62°C (dec.) [lit. (10) 255°C]. Analysis. Calculated forCl2H602N2: 68.57% C, 2.88% H, 13.33% N. Found: 68.43% C, 2.93% H, 13.32% N. NMR, infrared, and mass spectra are consistent with the desired product.PKa values of the conjugate acids of HI and III were determined spectrophotometrically at 30°C. The ionic strength, u, for both II and HI was 0.1. Equilibrium constants for the addition of hydroxide to H and IH were determined spectrophotometrically at ,u = 1.0. Stability consta...

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Disulfides, sulfenyl chlorides, thiosulfonates, and sulfensuccinimides were evaluated as electrophilic thiating agents for converting the enamine 6-dehydrodeoxynupharidine to α-thiohemiaminal derivatives of the alkaloid deoxynupharidine. Sulfensuccinimides were generally the most useful but other types of agents produced better yields in some individual cases.