The first chemical synthesis of D-eryrhro-sphingosine-l-phosphate (which occurs naturally) is described. This synthetic product had an inhibitory effect on motility of mouse melanoma B16/Fl cells in an in vitro assay system. Sphingosine-l-phosphate (SPN-1-P) has been known for many years as an intermediate product during degradation of sphingosine (SPN) by SPN kinase to ethanolamine-l-phosphate and a long-chain aldehyde (e.g., palm&al) by a pyridoxal phosphate-dependent lyase reaction 1. The biological significance of SPN-1-P has been reported recently2. However, its physiological function in cells remains unclear, except for its Ca2+ mobilizing activity in some cells 2c. Recently, we demonstrated that SPN-1-P inhibits motility of melanoma cells at a very low concentration (10 nM), at which SPN, N,N-dimethyl-SPN, and N,N,N-trimethyl-SPN have no inhibitory effect3. Furthermore, SPN-1-P is far less cytotoxic than these other three compounds, and does not inhibit protein kinase C. These biological findings suggest that SPN-1-P may act as an agent for prevention of tumor cell metastasis and inflammatory processes, both of which are highly dependent on cell motility. Unlike SPN and its N-methylated derivatives, the chemical synthesis of SPN-1-P has not been reported. The only known method for preparation of SPN-1-P is by treatment of sphingosylphosphocholine (SPC) with phospholipase D from Streptomyces chromofuscus, which gives a mixture of D-erythro and L-threo isomers. During design and synthesis of cell motility inhibitors derived from SPN-l-P, we developed a chemical synthesis of D-erythro-SPN-l-P, the naturally occurring isomer.