Abstract
Silicatein-α (Silα), a hydrolytic enzyme derived from siliceous marine sponges, is one of the few enzymes in nature capable of catalysing the metathesis of silicon–oxygen bonds. It is therefore of interest as a possible biocatalyst for the synthesis of organosiloxanes. To further investigate the substrate scope of this enzyme, a series of condensation reactions with a variety of phenols and aliphatic alcohols were carried out. In general, it was observed that Silα demonstrated a preference for phenols, though the conversions were relatively modest in most cases. In the two pairs of chiral alcohols that were investigated, it was found that the enzyme displayed a preference for the silylation of the S-enantiomers. Additionally, the enzyme’s tolerance to a range of solvents was tested. Silα had the highest level of substrate conversion in the nonpolar solvents n-octane and toluene, although the inclusion of up to 20% of 1,4-dioxane was tolerated. These results suggest that Silα is a potential candidate for directed evolution toward future application as a robust and selective biocatalyst for organosiloxane chemistry.
Highlights
During the multi-step chemical synthesis of complex molecules, silyl ethers are often employed for the protection of hydroxyl groups [1,2,3,4,5,6,7], where their utility arises from orthogonality to other commonly used acid- and base-labile protecting groups
A survey into the reactivity of TF-Silα-Strep with a selection of aromatic and aliphatic alcohols has been conducted. These enzymatic silyl condensations show a preference for aromatic alcohols over aliphatic alcohols, as evidenced by much higher net conversions
Greater improvements in conversions were achieved with the chiral aliphatic alcohols, as quantified by the fold increase, since the uncatalysed reactions with these alcohols showed proportionally much lower levels of product formation
Summary
During the multi-step chemical synthesis of complex molecules, silyl ethers are often employed for the protection of hydroxyl groups [1,2,3,4,5,6,7], where their utility arises from orthogonality to other commonly used acid- and base-labile protecting groups. In all cases, the necessary reagents are energy intensive to produce, and their use results in the generation of stoichiometric amounts of by-products that are hazardous or environmentally undesirable (e.g., triflic acid, hydrogen chloride, hydrogen). In this regard, the capability of silylate hydroxy groups through the condensation of the corresponding silanol and alcohol would circumvent the need for harsh reagents and only release water
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