L-​Glutamine and glutamic acid were incorporated in a tetrahydro-​2H-​1,​3,​5-​thiadiazine-​2-​thione (THTT) skeleton contg. different alkyl, cycloalkyl and aralkyl groups at N3 of the ring system.  These THTT derivs. revealed high lipophilicity compared with L-​glutamine and glutamic acid.  The degrdn. kinetics were studied -​in vitro- using aq. buffer solns. of pH values: 1.2, 6.0, 7.4, 7.8 and 9.0 at 37°.  From the pH profile, the degrdn. was accounted for, in terms of specific base-​catalyzed reactions.  All of the compds. however, showed higher acid-​stability.