Bombyx Mori Silk Fibroin as a Sustainable Organocatalyst for Diastereoselective Michael Additions

Powdered silk fibroin (PSF) extracted from Bombyx mori cocoons is reported as a heterogeneous organocatalyst in the selective Michael 1,4 addition of nitromethane to α,β-unsaturated carbonyl compounds, affording Michael adducts in almost quantitative yields, with complete antidiastereoselectivity and in mild conditions. PSF proved to be reusable for more than 50 recycles without any loss of catalytic activity. In silico studies suggest the presence of an enzyme-like pocket as the active catalytic site, pointing out fibroin fibers as a heterogeneous biological organocatalyst.