Octa-O-bis-(R,R)-Tartarate Ditellurane (SAS) - a novel bioactive organotellurium(IV) compound: synthesis, characterization, and protease inhibitory activity.

Octa-O-bis-(R,R)-Tartarate Ditellurane (SAS) is a new Te(IV) compound, comprised of two tellurium atoms, each liganded by four oxygen atoms from two carboxylates and two alkoxides of two tartaric acids. Unlike many other Te(IV) compounds, SAS was highly stable in aqueous solution. It interacted with thiols to form an unstable Te(SR)(4) product. The product of the interaction of SAS with cysteine was isolated and characterized by mass spectroscopy and elemental analysis. SAS selectively inactivated cysteine proteases, but it did not inactivate other families of proteolytic enzymes. It displayed selectivity towards the cysteine protease cathepsin B, a human enzyme of pharmaceutical interest, with a second order rate constant k(i)/K(i)=5900 M(-1) s(-1).