Synthesis of a d- -lecithin, an active antigen component in the serodiagnosis of syphilis.

Although the serodiagnosis of syphilis by various tests has been carried out routinely for many years, our knowledge concerning the chemical nature of the specific antibody and antigen is still too limited to allow a satisfactory interpretation of the serological reactions involved. Valuable contributions towards the elucidation of the structure of several constituents of the antigen have been made during the past 10 years by Pangborn, who succeeded in purifying and identifying two of the components, cardiolipin (1) and lecithin (2), and more recently by Rice and Osler (3), who achieved the isolation of a chromatographically homogeneous, immunologically active lecithin from a commercially available beef heart lecithin prepared for serological tests. Baer and Kates (4, 5) reported 2 years ago the synthesis of several constitutionally and configurationally pure L-a-lecithins. Subsequently Rosenberg (6), Kline (7), and Allen’ demonstrated that these synthetic lecithins, especially the L-cu-(dimyristoyl) lecithin (7), can replace advantageously the “purified lecithin of beef heart” as an antigen component in the serodiagnosis of syphilis.2 It was deemed of interest to study the effect of structural variations in the lecithin molecule on its activity as an antigen component. Several relevant facts have recently emerged. We now know, for instance, that the antigen activity of lecithin does not change appreciably (6, 7) if the unsaturated fatty acids are replaced by saturated fatty acids of varying chain length (Cl, + C&, but that the activity disappears altogether if the phosphoric acid-choline ester linkage is broken. The serological significance of this linkage became apparent when attempts to replace the lecithin component of the antigen with the