Functional Modeling of Cobalamine-Independent Methionine Synthase with Pyrazolylborate−Zinc−Thiolate Complexes

Abstract

A series of new pyrazolylborate-zinc-thiolate complexes Tp(Ph,Me)Zn-SR and Tp(Me,Me)Zn-SR, including two homocysteine derivatives, were prepared and structurally characterized. Their reactions with methyl iodide in nonpolar media resulted in the formation of the thioethers MeSR, including two methionine derivatives, and Tp(R',Me)Zn-I in all cases. Methylation of the thiolates could also be achieved with dimethyl sulfate and trimethylsulfonium iodide but not with trimethyl phosphate or N-methylpyridinium salts. The accumulated evidence indicates that the methylation occurs intramolecularly, i.e., at the zinc-bound thiolates: (i) The reactions occur readily in nonpolar media. (ii) Thiolate exchange at Tp(Ph,Me)Zn-SR with [PPN]SR' is slower than thiolate alkylation. (iii) The methylation of Tp(Ph,Me)Zn-SBn with MeI is a clean second-order reaction with k'' = 1.75 x 10(-2) M(-1) s(-1) at 300 K.

Coordination Polymers and Metal Organic Frameworks Derived from 1,2,4-Triazole Amino Acid Linkers

“…were also conducted because of their various binding and bridging modes [26][27][28][29][30][31][32][33]. Not surprisingly, in a short course, biomolecules and natural products like amino acids [34][35][36][37][38][39][40][41][42][43][44][45][46], peptides [47], proteins [46], nucleobases [48], magnesium formates [49], carbohydrates [47], metal glutarates [50,51], γ-cyclodextrin [36] leaped into this mainstream as attractive precursors and soon tributaries like metal-peptide frameworks (MPFs) [47], metal-biomolecule frameworks (MBioFs) [46][47][48] surfaced out and established their niche.…”

“…Among them the perceptible appearance of amino acid derivatives in recent years, either as metal-based molecular entities or oligomeric scaffolds in MOFs or CPs, justify their inclusion in the synthon/tecton library [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. In this frame, structure and reactivity of different amino acids in their natural or derivatized form were extensively studied.…”

“…In this frame, structure and reactivity of different amino acids in their natural or derivatized form were extensively studied. Relevant examples include proline [34,35], glycine [34], valine [36], alanine [37], aspartic acid [38], glutamic acid [36], phenyl alanine [39], histidine [40], methionine [41][42][43][44] and typtophan [36][37][38][39][40][41][42][43][44][45].…”

“…Advantages of amino acids are their natural framework with rich functional groups, which is amenable to derivatization thereby offering intriguing topologies when inserted as building blocks in supramolecular hierarchical self-assemblies [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. Indeed, thanks to their genuine chirality (except glycine) and electronic asymmetry, amino acid derivatives are considered as a preeminent choice to introduce asymmetry in MOFs to direct the network construction.…”

Synthetic modeling of zinc thiolates: Quantitative assessment of hydrogen bonding in modulating sulfur alkylation rates

“…The reaction of [Zn(SPh) 4 ] 2Ϫ with phosphotriesters was kinetically consistent with a dissociative pathway entailing deligation of thiolate from zinc before alkylation. In contrast, a number of laboratories have demonstrated that zinc thiolate complexes are cleanly alkylated by carbon electrophiles via a S N 2 pathway, with the ''bound'' thiolate serving as nucleophile (15)(16)(17)(18). Clearly, the nature of the zinc complexes and the medium used profoundly effect the course of these reactions.…”