5 '-Deoxy-5'-S-(3-methylthiopropylamine) sulfoniumadenos~ ne, the biological precursor of spermidine, has been synthesized by the condensation of 2', 3'-isoprop~ lidene-5'-toluene-p- sulfonyladcnosine and 3-thiopropylamine followed by removal of the acetonide group and subsequent methylation of the thioether. The corresponding (2-methylthioethy1amine)-and (4-methylthiobuty1aniine) sulfoniun~ adenosine derivatives have been prepared in a ...