PHYSICAL PROPERTIES OF FATS AND OILS 271 



symmetrical (a-) monoglycerides, the unsymmetrical (a,|S-) diglycerides, as 

 well as the symmetrical (a, a'-) diglycerides containing different fatty 

 acids. It may also result in the case of the triglycerides where two dif- 

 ferent acyl groups are introduced into the a- and a'-positions. 



Because of the large proportion of mixed triglycerides which exist in 

 natural fats and oils, it would appear highly probable that many optically 

 active triglycerides are present. One would expect this to be of con- 

 siderable importance in explaining the activity of the lipases, since their 

 action is highly selective insofar as optical isomers are concerned. ^^^ 

 Although optically active a-glycerol phosphate and phospholipids have 

 been known for a long period, optically active enantiomorphs have not 

 been observed among the triglycerides composed of the longer fatty acid 

 chains. The difficulties in isolation are considerable, since the procedures 

 employed in such isolation might be expected to destroy any asymmetry 

 that was present, by such changes as migration of the acyl groups. More- 

 over, because of the low order of rotation w^hich has been observed for 

 kno\m asjonmetric glycerides, one might expect quite low values for nat- 

 ural products, which are mixed with considerable amounts of inactive 

 material. Most of our information about optically active glycerides has 

 therefore been derived from synthesis of representative compounds rather 

 than from examination of products isolated from natural sources. 



The original terminology of the glycerides employed by Abderhalden 

 and Eichwald^^^ was to prefix the name of the compound with d- or l- 

 according to its rotation. However, the nomenclature adopted more re- 

 cently by Fischer and Baer^^* is to relate them to the corresponding c^- 

 and Z-glj'ceraldehydes, similar to the current nomenclature for the sugars. 



a. Synthesis of Optically Active Glycerides. The earlier procedures for 

 preparation of the optically active antipodes involved resolution of the 

 enantiomorphs from racemic mixtures. Care had to be taken at all 

 stages to avoid racemization by the acid or basic residues which were in- 

 troduced to render such separations possible. Abderhalden and Eich- 

 wald^*^ prepared optically active a-monoglycerides and a:,/3-diglycerides^^^'3^^ 

 from the optically active forms of l-amino-2,3-dibromopropane which 

 were resolved by means of c?-tartaric acid. Bergmann and Sabetay^" 

 carried out the resolution of the a-acyl esters of 7-aminopropylene glycol 

 with saccharic acid, followed by treatment with nitrous acid to prepare 

 the optically active monoglyceride. The Q:,|8-diacyl esters of 7-amino- 

 propylene glycol were employed to prepare the enantiomorphs of a,^- 



"^ E. Baer and IT. O. L. Fischer, /. Biol. Chem., H5, 61-68 (1M2). 

 M» E. Alxlerhalden and E. Einhwald, Ber., J^7, 1856-1866 (1914). 

 '»« H, O. L. Fischer and E. Baer, Chem. Revs., 29, 287-316 (1941). 

 •^»» 10. Abderhalden and E. Eichwald, Ber., 48, 113-117 (1915). 

 »«•> E. Al)derhaklen and E. Eichwald, Ber., 48, 1847-1865 (1915). 

 »'•" M. Bergmaun and S. Sabctay, Z. physiol. Chem., 137, 47-61 (1924). 



