Synthesis and characterization of selenium(I/II) and tellurium(IV) derivatives of amino acids

Abstract

The direct reaction between Te metal and methyl 2-(2-bromoacetamido)propanoate (27) at room temperature, yields the first example of organotellurium(IV) derivative (MeOC(O)CH(Me)NHCOCH2)2TeBr2 (31). Similarly, reaction of Te with methyl 2-(2-bromoacetamido)acetate (26) and methyl 2-(2-bromoacetamido)-3-phenylpropanoate (28) in presence of NaI in acetone gives MeOC(O)CH2NHCOCH2I (29), MeOC(O)CH(R)NHCOCH2)2TeI2 (R = H (30) and CH2Ph (32). Treatment of 26/27/28 with Li2Te2/Li2Se2 readily provides the [MeOC(O)CH(CH3)NHCOCH2]2Te2, (33); [MeOC(O)CH2NHCOCH2]2Se2, (34); [MeOC(O)CH(CH2Ph)NHCOCH2]2Se2, (35) and ▪ (36). Similarly the reaction of (2,6-dimethyl-4-tert-butylC6H2)SeNa with 28 readily provide the [MeOC(O)CH(CH2Ph)NHCOCH2]SeC6H2-2,6-dimethyl-4-tert-butyl), (37) in good yield. Molecule [MeOC(O)CHNH(Boc)CH2]2Se2, (38) and [NaOC(O)CHNH(Boc)CH2Te(2,4,6-Me3C6H2] (39) were prepared by the treatment of Li2Se2/2,4,6-Me3C6H2TeNa with methyl 3-bromo-2-((tert-butoxycarbonyl)amino)propanoate and N-(t-Boc)-l-serine β-lactone respectively. These compounds are purified by chromatography and characterized by a number of analytical techniques such as (1H, 13C, 77Se and 125Te NMR) spectroscopy, mass spectrometry and elemental analysis. The single crystal X-ray studies of 29, 30, 31, 36 and 38 revealed the presence of characteristic O⋯Se/Te, secondary bonding interactions. A detailed analysis of the crystal structures of the compound reveals interesting supramolecular assembly.