Elektronenreiche Heterocyclen mit Thiophosphinamid‐, Carboxamid‐, <i>O</i>‐Silylurethan‐ und <i>O</i>‐Silylisoharnstoff‐Funktionalität. Synthese, Spektren, chemische und elektrochemische Reaktivität

Bessenbacher, Christian; Kaim, Wolfgang; Stahl, Thomas

doi:10.1002/cber.19891220523

Cited by 16 publications

(1 citation statement)

References 45 publications

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“…' Pyrazine itself, and quinoxaline, have been converted ' into 1,4-dihydro-1,4-bistrimethylsilyl derivatives 4a and 5 using a combination of lithium and trimethylsilyl chloride, and 4a, by further reaction with carbon dioxide, was converted into bisurethane 4b. 19 Electrolytic reduction of pyrazine in the presence of acylating agents afforded acylated dihydro derivatives 4c,20 but electrolytic reduction of quinoxaline followed by attempted trapping with acylating agents led only to polymeric material, though 2-phenyl-and 2,3-diphenylquinoxalines gave 1 ,4-bis-and 1(4)-mono-methoxycarbonyl-1,4-dihydroquinoxalines.' ' For our synthetic ambitions, we felt that a borohydride-based process would be much more suitable than either metal-based or electrolytic reductions, and would have the added bonus of avoiding the necessity for handling tetrahydropteridines (vide supra).…”

Section: Introductionmentioning

confidence: 99%

Model studies related to the cofactor of oxomolybdoenzymes. Part 4. Reduction of the pyrazine ring in quinoxalines and pteridines

Russell¹,

Garner²,

Joule³

1992

J. Chem. Soc., Perkin Trans. 1

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Reduction of quinoxalines and pteridines with sodium borohydride or sodium cyanoborohydride in the presence of benzyl chloroformate gives Nbenzyloxycarbonyl-or N,N'bisbenzyloxycarbonyl tetrahydro derivatives. BackgroundAll the oxomolybdoenzymes except nitrogenase, including xanthine oxidase, aldehyde oxidase, sulfite oxidase and nitrate reductase, contain a common cofactor, Moco which has been shown to have molybdenum coordinated via two sulfurs in an organic portion which includes a pterin, the complete organic unit being termed molybdopterin. There is evidence' that the pyrazine ring in the pterin is in a reduced state, earlier views being that it is at a tetrahydro level but the most recent work3 suggesting that molybdopterin is a dihydropterin, has a quinonoid tautomeric form, and that therefore partial structure 1 represents Moco. It is relevant to note that a tetrahydropterin is the cofactor for monoamine-synthesising monooxygena~es.~The absolute configuration of the side-chain hydroxy-bearing carbon has been deduced to be that shown in 1, on the basis of a CD comparison between samples of alkyne 2 produced in homochiral form by total synthesis,' and by degradation of the enzyme, respectively.6 which regioselective reductions are carried out to produce 1,2,3,4-tetrahydroquinoxalines and 5,6,7,8-tetrahydropteridines, stabilised by (removable) protection in such a way as to facilitate our synthetic work towards molybdopterin and Moco.Other workers have shown that catalytic reductions "-14 of pteridines give 5,6,7,8-tetrahydro derivatives, which are oxygenlabile; ' sodium dithionite treatment leads to 7,8-dihydro derivatives. '' Acylation of tetrahydropteridines at N-5 produces air-stable compound^,'^ but care is needed, for N-5ethylation has been observed under vigorous acetylation conditions.'2 An elegant method for the partial reduction of pyridines, which also allows isolation of unstable dihydro products in protected/stabilised form, was introduced by Fowler,16 who found that treatment of pyridine with sodium borohydride in the presence of methyl chloroformate gave a mixture of 1methoxycarbonyl-1,2-and -1,4-dihydropyridines thus stabilised as urethanes. 1 2Since it is likely that the mode of action of Moco involves redox processes at the metal centre, possibly linked to changes in the pyrazine ring oxidation level, we have previously reported synthetic studies on quinoxalines carrying 1,2-disulfur-substituted side-chains at C-2,1.798 the complexation9 of some of these products with molybdenum, tungsten, vanadium and cobalt as models for the situation in Moco, and electrochemical studies l o on [Co(q5-C5H,)(S2CRH)] (where R = quinoxalin-2-yl).

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Section: Introductionmentioning

confidence: 99%