Compounds of the formula ##STR1## wherein each of one or two R is independently ##STR2## wherein n is an integer from 4 to 18, each R.sub.1 ' and R.sub.2 ' is independently H, alkyl (1-4C) or alkenyl (1-4C); and R.sub.3 ' and R.sub.4 ' are independently H or CH.sub.3 ; and wherein the alkyl or alkenyl may be substituted by a hydroxyl, halo or dimethylamino group and/or interrupted by an oxygen atom, H or alkyl (1-4C), including resolved enantiomers and/or diastereomers and mixtures thereof. Preferably, n is from 6 to 10, R.sub.1 ' and R.sub.2 ' are independently H or methyl and R.sub.3 ' and R.sub.4 ' are H. In particular, the compounds lower elevated levels of unsaturated, non-arachidonate phosphatidic acid (PA) and diacylglycerol (DAG) derived from said PA within seconds of the primary stimulus and their contact with said cells. The modulatory effect depends on the nature of the target cell and the stimulus applied.