Methyl hexahydro-3-methyl-Gthioxwl,2,4,5-tetrazine-3nonanoate (I) on treatment with reagents such as chloroacetic acid, 1,2-dibromoethane and 2-mercaptoethanol under different reaction conditions afforded methyl 3,4,6,7-tetrahydro~methyl4~oxw2H_-thiazolo[3,2-b]-l,2,4,~ tetrazine-3-nonanoate (II), methyl 3,4,6,7-tetrahydrw3methyl-2H_-thiazolo[3,2-b] -1,2,4,~tetrazine~?~nonanoate (III) and methyl 8-methyl-l-oxa~-thia-6,7,9,10-tetraazaspiro-[4.5]-decane-8-nonanoate (IV) in good yields. The structures of compounds II-IV were established by elemental analysis, infrared (IR), nuclear magnetic resonance (NMR), and mass spectral data.KEY WORDS: Chloroacetic acid, 1,2-dibromoethane, 2-mercapt~ ethanol, methyl hexahydro-3-methyl-6-thioxo-l,2,4,5-tetrazine-3nonanoate, methyl 8-methyl-l~xa-4-thia4},7,9,10-tetraazaspiro[4.5]decane-8-nonanoate, methyl 3,4,6,7-tetrahydro-3-methyl-6-oxo-2Hthiazolo[3$-b]-l,2,4,5-tetrazine-3-nonanoate, methyl 3,4,6,7-tetrahydro-3-methyl-2H_-thlazolo [3,2-b]-l,2,4,5-tetrazine-~nonanoate.