The new derivatives 7a--c. of vitamin B,2, with a peripheral tris(oxyethy1ene) chain linked to the corrin ring by an amide or ester group, are prepared, and their ligand-exchange reactions are investigated. Upon reduction of the aqua-cyano complexes 8a-c with NaBH,. cleavage of the 'outer' ester and amide group IS observed.Introduction. -We are interested in models for vitamin-B , ,-dependent rearrangements that mimic the apoenzyme-substrate interaction [I -61. In our first model, the vitamin-B, , derivative catalyst and the substrate were modified by aliphatic side chains for association with each other by noncovalent interactions in appropriate solvents [7] [8].It has been shown that this peripheral association between the catalyst and the substrate enhances the methylmalonyl-succinyl rearrangement in aqueous methanol. In the adenine-thymine model, it has been demonstrated that the base pairing, used as recogni-
Several multifunctional derivatives of methylthiomalonic acid ( 2-(thiocarboxy)acetic acid), i.e. 20a, b, 21, 22a, b, and 24, were prepared from thiols bearing a functionalized head group, i.e. from 9a, b, 12, and 16d, f (Schemes 4 and 5). The association constants of the two dithio podands 8b and 11 with K were determined.Introduction. ± For development of models of the coenzyme-B 12 -dependent methylmalonyl-CoA mutase, we have prepared a variety of (bromomethyl)methylthiomalonates ( 2-(bromomethyl)-2-methyl-3-oxo-3-(alkylthio)propanoates) with head groups for molecular recognition. These model substrates are to be used to investigate the efficiency of the methylmalonyl-succinyl rearrangement when the substrate and the vitamin-B 12 molecule are held together by noncovalent interactions. The concept of enhancing the rearrangement by peripheral association of appropriate groups is based on the idea that enzymes or enzyme-coenzyme complexes must recognize their substrates and associate with them through noncovalent bonds to provide the orientation and proximity necessary for catalysis [1 ± 4]. Hitherto, we have reported a hydrophobic model, where lipophilic alkane chains are used for the association between the methylmalonyl moiety and the vitamin B 12 , appropriately modified in the periphery, and two models based on association in aprotic solvents between an A´T and a C´G base pair, respectively [5 ± 8]. Enhanced rearrangement has been observed for the hydrophobic and the A´T mode [5] [6]. In further persuit of vitamin-B 12 -related concepts for molecular recognition between methylmalonyl substrates and the catalyst, we considered the association between polyether (podand) units mediated by cations as well as the interaction between carbohydrate-derived units. We report here the preparation of alkanethiols bearing a polyether moiety or a pentahydroxyhexanoyl head group as well as the efficient synthesis of thioesters thereof. First results for the binding constants between two polyethers with alkali cations are reported.
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