Selenite (H(2)SeO(3)) reacts with thiol compounds (RSH) under acidic conditions to form selenotrisulfides (RSSeSR, i.e. monoselenodithiols). The stoichiometry of the reaction is proposed as 4RSH+H(2)SeO(3)-->RSSeSR+RSSR+3H(2)O. Surprisingly, we found novel polynuclear selenium-containing compounds, i.e. polyselenodipenicillamines (PenSSe(2-4)SPen), in the reaction of D-penicillamine (PenSH) with H(2)SeO(3). The selenium-centered features of PenSSe(2-4)SPen were determined by (1)H-NMR and LC-MS/MS analyses, showing that the selenium isotope abundance patterns of the compounds were in good agreement with the theoretically-calculated ones. In order to better understand the mechanisms for PenSSe(2-4)SPen production, various molar ratio of H(2)SeO(3) (1/8 to 4 times of PenSH) was reacted with PenSH, and the concentration of the products was calculated from integral values of dimethyl proton signals for PenSSe(1-2)SPen as compared with methyl proton signals for acetic acid (an internal standard). Total PenSSe(1-2)SPen concentration was increased with increasing of H(2)SeO(3), in which concomitant decrease of PenSSPen (disulfide form of PenSH) was observed. Based on these results, we proposed the PenSSe(2-4)SPen production mechanisms being involved in penicillamine selenopersulfides (PenSSe(1-2)H).