sn-

Prefix meaning stereospecifically numbered; a system of numbering the glycerol carbon atoms in lipids, so that the locant numbers remain constant regardless of chemical substitutions, as opposed to systematic numbering.

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[for stereospecific numbering] a chemical prefix used to indicate stereoisomers of glycerol derivatives: the glycerol chain is numbered as if it were derived from L-glyceraldehyde. This provides an unambiguous numbering. The enantiomer is obtained by reversing the numbering. For example sn-glycerol 1-phosphate is the same as L-glycerol 1-phosphate; the enantiomer D-glycerol 1-phosphate is the same as L-glycerol 3-phosphate or sn-glycerol 3-phosphate. See D-.