Phytochemical analysis, antioxidant and hypoglycemic activities of a methanol extract from <i>Stachys brachyclada</i> de Noé ex Coss. leaves

Stachys brachyclada de Noé ex Coss. (Lamiaceae) is a quite rare medicinal plant endemic to the Mediterranean basin. In this study, seven secondary metabolites from a methanol extract of its leaves have been isolated and identified by a combination of chromatographic and spectroscopic methods (1D and 2D NMR experiments and ESIMS analysis). They include one ethyl 4-hydroxybenzoate (1), three acylated flavone glycosides (2–4), one diapigenin derivative (5) and two flavone aglycones (6–7). Stachysetin (5) was found the major compound of the extract (74.0 mg/g of dry matter). Moreover, the produced extract showed the ability in inhibiting the α-glucosidase enzyme (IC50 = 13.7 µg/mL), in quenching the radical 1,1-diphenyl-2-picrylhydrazyl (EC50 = 74.6 µg/mL), and in reducing the intracellular oxidative stress level in Human Dermal Fibroblast (64% inhibition at 50 µg/mL).</p

Routes to Covalent Catalysis by Reactive Selection for Nascent Protein Nucleophiles

Reactivity-based selection strategies have been used to enrich combinatorial libraries for encoded biocatalysts having revised substrate specificity or altered catalytic activity. This approach can also assist in artificial evolution of enzyme catalysis from protein templates without bias for predefined catalytic sites. The prevalence of covalent intermediates in enzymatic mechanisms suggests the universal utility of the covalent complex as the basis for selection. Covalent selection by phosphonate ester exchange was applied to a phage display library of antibody variable fragments (scFv) to sample the scope and mechanism of chemical reactivity in a naive molecular library. Selected scFv segregated into structurally related covalent and noncovalent binders. Clones that reacted covalently utilized tyrosine residues exclusively as the nucleophile. Two motifs were identified by structural analysis, recruiting distinct Tyr residues of the light chain. Most clones employed Tyr32 in CDR-L1, whereas a unique clone (A.17) reacted at Tyr36 in FR-L2. Enhanced phosphonylation kinetics and modest amidase activity of A.17 suggested a primitive catalytic site. Covalent selection may thus provide access to protein molecules that approximate an early apparatus for covalent catalysis