Biosynthesis of Phytosphingosine

Dihydrosphingosine-4,5-3H was synthesized via the catalytic tritiation of N-carbobenzoxysphingosine. The tritium activities on carbon atoms 4 and 5 were 47 and 37%, respectively; the remainder of 16% on carbon atoms 6 to 18 was due to double bond migration, or carbon-bonded hydrogen exchange, or both. Radiochemical impurities of high specific activity were formed during the synthesis and were detected with iodine vapor after thin layer chromatography. They did not act as a substrate for phytosphingosine biosynthesis. From the ratio of isotope in substrate and product, it was concluded that dihydrosphingosine-4,5-3H was utilized intact in the formation of phytosphingosine. N-Acetyldihydrosphingosine-4,5-3H, N-acetyl-1-14C-dihydrosphingosine-4,5-3H, and triacetyldihydrosphingosine-4,5-3H did not serve as substrates for the synthesis of phytosphingosine. It was suggested that this was due to the low solubility of these compounds rather than to the absence of the appropriate enzymes.