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Total synthesis of stereospecific sphingosine and ceramide

1978; Elsevier BV; Volume: 19; Issue: 2 Linguagem: Inglês

10.1016/s0022-2275(20)41565-2

1539-7262

Yukihiro Shoyama, Hikaru Okabe, Yasuo Kishimoto, Catherine E. Costello,

Lysosomal Storage Disorders Research

A small-scale synthesis of the four sphingosine stereoisomers (D-erythro, L-erythro, D-threo, and L-threo) and lignoceroyl D- and L-erythro-sphingosines, which is suitable for synthesis of tritium-labeled compounds, is described. Ethyl ~~-erythro-2-acetamino-3-hydroxy-4t-octadecenoate was esterified with L( +)-acetylmandeloyl chloride and the two diastereomers obtained were separated from each other by thin-layer or column chromatography. Each diastereomer was subjected to ethanolysis to obtain ethyl D- or ~-erythro-2- amino-3-hydroxy-4t-octadecenoate which was then reduced with LiAlH, or NaBH, to yield D- or L-rrythro-sphingosine. D- erythro-( l-3H)Sphingosine with high specific activity was pre- pared by using LiAPH, in the last step. D- and L-threo- sphingosines were synthesized from ethyl DL-threo-2- acetamino-3-hydroxy-4t-octadecenoate by using a similar procedure. Ceramide (lignoceroyl sphingosine) was prepared either by acylating sphingosine or by the following new method. Ethyl ~~-erythro-2-amino-3-hydroxy-4t-octadecenoate was converted to the N-lignoceroyl derivative and esterified with L( +)-acetylmandeloyl chloride. The two diastereomers obtained were separated and each isomer was treated with a catalytic amount of sodium ethoxide. One of the products, ethyl ~erythro-2-lignoceroylamino-3-hydroxy-4t-octadeceno- ate, was reduced with NaBH, to yield ceramide. N-palmitoyl m-eryfhro-sphingosine was also prepared using an identical procedure. N-lignoceroyl D-erythro-( l-3H)sphingosine was prepared by NaB3H, reduction of the corresponding amide ester. A doubly labeled ceramide, ( l-14C)lignoceroyl ( 1- 3H)sphingosine, containing high specific activity, was prepared by mixing the above N-lignoceroyl D-erythro-( 1- 3H)sphingosine and N-( l-14C)lignoceroyl D-erythro-sphingo- sine. The conversion of the doubly labeled ceramide to 3- keto derivative is also described. Supplementary key words Resolution of ethyl D- and L-erythro -2- acetamino-3-(~(+)-acetylmandeloyloxy)-4~-octadecenoate . resolu- tion of D- and ~-erythro-2-lignoceroyl amino-3-(~( +)-acetylmandeloyl- oxy)-4t-octadecenoate . ( l-3H)sphingosine . N-acyl ( I-3H)sphingo- sine . doubly labeled ceramide . NaBH, reduction of ethyl 2- acylamino-3-hydroxy-4t-octadecenoate * doubly labeled 3-ketocer- amide Ceramide (N-acyl-D-erythro-sphingosine) is a key in- termediate in the biosynthesis and degradation of sphingolipids (1, 2). It is synthesized in vitro from sphingosine and fatty acyl CoA (3-5) or a free fatty acid (6) and hydrolyzed to free fatty acid and sphingosine (6, 7). Sphingosine is synthesized from palmitoyl CoA and serine. These compounds are first condensed to 3-ketodihydrosphingosine; this is fol- lowed by dehydrogenation at the 4,5-position and reduction of the 3-keto group (1, 8). Recently, Morel1 and Radin (4) reported that rat brain microsomes catalyze the condensation of 3-ketodihydrosphingosine with acyl CoA to form N-acyl 3-ketodihydrosphingo- sine. This observation suggests a new pathway of ceramide synthesis in which the dehydrogenation and reduction of 3-ketodihydrosphingosine occur after it is converted to the N-acyl derivative. To test this hypothesis, the synthesis of a doubly labeled 3- ketoceramide, as well as of a doubly labeled ceramide, becomes necessary.