Synthesis and Enzymatic Conversion of Amino Acids Equipped with the Silanetriol Functionality: A Prelude to Silicon Biodiversification

Abstract

Synthetic routes are reported for the three analogues of the simplest L-2-amino-dicarboxylic acids, aspartate, glutamate, and aminoadipate, in which the silanetriol group (Si(OH)₃) replaces the distal carboxyl group (CO₂H). Direct access to the silanetriol amino acids relied either on catalytic hydrosilylation of a terminal alkene using triethoxysilane, or on alkylation of a glycine equivalent anion by triallyl(iodomethyl)silane. In both cases, acid hydrolysis afforded the silanetriol amino acids. These were shown to self-assemble into siloxane Si-O clusters as their concentration in water increased in the pH range of 1–12. Such reversible cross-linking did not prevent silanetriol amino acids from serving as substrates of an aminotransferase enzyme, boding well for their utilization as microbial nutrients to encompass silicon in future stages of metabolism and polypeptide edifices.