Synthesis and Biological Activities of Substituted 2-Alkoxy-1,3,2-thiazaphospholidine 2-Sulfides

4-Isobutyl-2-methoxy-l,3,2-thiazaphospholidine 2-sulfide (iBMTS) and the related thiazaphospholidines were prepared by reacting phosphorodichloridothionate and /?-aminothiols, which were obtained from the corresponding /?-aminoalcohols via /?-aminoalkyl hydrogen sulfate and 2-mercaptothiazoline followed by hydrochloric acid-catalyzed hydrolysis. Thiazaphospholidines had a higher insecticidal activity than the corresponding oxazaphospholidines against female Musca domestica houseflies by topical application. Methoxy derivatives were more potent insecticides than ethoxy derivatives. Oxazaphospholidines with a more bulky hydrophobic branched-alkyl substituent at C₄ or phenyl at C₅ were more potent than those with a less bulky hydrophobic substituent. In thiazaphospholidines, however, the effect of introduction of a bulky hydrophobic substituent at C₄ was not as significant as in oxazaphospholidines in increasing the insecticidal activity. Neither oxazaphospholidines nor thiazaphospholidines activated adenylate cyclase of Periplaneta americana ventral-nervecord homogenates, but both reduced octopamine-stimulated adenylate-cyclase activity.