Stereospecific numbering

Diels-Alder reaction and. 494-495 El reaction and, 392 E2 reaction and, 387-388 R.S configuration and, 297-300 S 1 reaction and, 374-375 S -2 reactions and, 363-364 Stereogenic center, 292 Stereoisomers, 111 kinds of, 310-311 number of, 302 properties of, 306 Stereospecilic, 228, 494 Stereospecific numbering, sn-glycerol 3-phosphate and, 1132 Steric hindrance, Sjvj2 reaction and, 365-366 Steric strain, 96... 

We will use a shorthand designation for fatty acids, i.e., 18 0, stearic acid 18 1, oleic acid etc. The first figure is the number of carbons, the second the number of double bonds. To locate the fatty acids in acyl-glycerols, stereospecific numbering (sn) will be employed. If a glycerol molecule is drawn with the secondary hydroxyl to the left, the hydroxyl above is sn-1 and that below is sn-3. 

Naturally occurring glycerides are esters of xrt-glycerol, where sn stands for stereospecific numbering according to the 1UPAC nomenclature for lipids. The... 

The stereodescriptor sn indicates that the name results from the convention of stereospecific numbering of the atoms of glycerol. The structure must therefore be drawn as a Fischer projection formula with the l configuration. 

Figure 1.2. Fischer projection diagram of a triacylglycerol showing the stereospecific numbering (sn-) convention.

Figure 17.1. Fisher projection used in the stereospecific numbering of a triacylglyceride.

Figure 1 Structures of PIPn 1 -9. For stereospecific numbering of the glycerol moiety, see Reference 6. For stereospecific numbering of myo-inositol residue, see References (5) and (7).

A stereospecific numbering system (Sn) is used to indicate the location of specific fatty acids in triglyceride molecules such as in 1-stearoyl-2-oleoyl-3-myristoyl-Sn-glycerol the respective fatty acids are indicated in the 1, 2, and 3 positions. This kind of information is very valuable in relating properties of certain fats to compositional data. Table 4.4... 

Fatty acids in oils and fats are found esterified to glycerol. Glycerol (1,2,3-trihy-droxypropane) is a prochiral molecule. It has a plane of symmetry, but if the primary hydroxyls are esterified to different groups, the resulting molecule is chiral and exists as two enantiomers. The stereospecific numbering system is used to... 

Figure 1. A triacylglycerol molecule (R fatty acid moiety, sn stereospecific number).

Table 3.8. The chemical structure of glycerophospholipids. The generic term phosphatidyl- stands for l,2-diacyl-sn-glycero-3-phospho-, in which sn denotes stereospecific numbering (in the D/L nomenclature this corresponds to 2,3-dlacyl-D-glycero-l-phospho-). The OH-groups of the glycerol that are not bound to the head group are esterified to fatty acid.

The stereospecific numbering of acylglycerols has been introduced by H. Hirschmann (J. Biol. Chem. 235 (1960) 2762) and is widely accepted, although its application is limited. See H. Hauser. G. Poupart, in The Structure of Biological Membranes. P. Yeagle (Ed.), CRC Press, Boca Raton, Florida, 1992. 

---