On the biocatalytic cleavage of silicon–oxygen bonds: A substrate structural approach to investigating the cleavage of protecting group silyl ethers by serine-triad hydrolases

The biotransformation of compounds containing silicon has recently been a subject of much interest. In this study, a variety of commercially available serine hydrolases were tested for their ability to catalyse the hydrolysis of the silicon–ether bond in a variety of silyl ethers. The hydrolysis of trimethylethoxysilane in buffer was not found to be accelerated by the presence of trypsin, chymotrypsin, or a variety of other lipase and protease enzymes. Cleavage of a range of alternative silyl ether substrates, including a trimethylsilyl (TMS) ether, by these hydrolases was also not observed, but, interestingly, only two of the enzymes tested were able to cleave a t-butyl α,α,α-carboxylate that was approximately isosteric with the TMS-protected substrate. This suggests that the cleavage of Si–O bonds by serine hydrolases, such as the cathepsin homolog silicatein-α, may be in part limited by steric effects, as the reactive centre in the substrate is always, by analogy to C-centred substrates, tertiary, and thus inherently sterically demanding regardless of the putative catalytic competence of the enzymes.