Homochiral 1-O-alkyl and 1-O-acyl derivatives of myo-inositol 3,4,5-trisphosphate were designed and synthesized as novel analogues of phosphatidyl-myo-inositol 3,4,5-trisphosphate. 1-O-Octadecyl and 1-O-stearoyl analogues inhibited the synthesis of phosphatidyl-myo-inositol 3,4-bisphosphate from phosphatidyl-myo-inositol 3,4,5-trisphosphate catalyzed by PIns-3,4,5-P-3 5-phosphatase. These compounds may act as competitors in the enzyme reaction, suggesting that they may be useful in studies of the role of phosphatidyl-myo-inositol 3,4,5-trisphosphate as a candidate second messenger in cellular signal transduction.