Absolute Asymmetric Synthesis and Asymmetric Catalysis 1 07 



histological preparations of tissues, a case in point being the adsorption by malig- 

 nant tumours of the antipodes of the stain 



120]. 



It would seem that only by asymmetric adsorption on a protein, genetically 

 associated with the spiral structure of deoxyribonucleic acids, can one explain 

 the selective sorption of D-alanine by the walls of the blood vessels and many 

 other examples of the appearance of spiral structures in natural compounds of 

 high molecular weight [21]. 



The protein of wool is very effective in resolving racemic hydroxy acids. A 

 considerable degree of resolution was achieved by Marthin & Kuhn [22] by 

 passing a continuous ribbon of wool through a solution of mandehc acid. 



Bradley [23], also studying the asymmetric adsorption of mandelic acid and 

 its analogues on wool and casein, concluded that successful resolution was only 

 possible in the case of acids of which one antipode could form a superficial labile 

 salt by reacting with the basic groups of the protein. 



For analytical purposes the asymmetric adsorbents lactose, starch and espe- 

 cially the cellulose of paper, have had a great application. By using lactose in 

 Tsvet's chromatographic method a complete separation of the antipodes of 

 /)-phenylenebisiminocamphor was obtained (Henderson & Rule, 1938) [24]. 

 Great efficiency of resolution was seen, both in the case of Troger's base, con- 

 taining an asymmetric atom of tervalent nitrogen, and in that of DL-chloram- 

 phenicol [25]. 



A less effective method was adsorption on starch during chromatographic 

 separation of complex, racemic, cobalt compoimds [26]. Only in the case of cobalt 

 triethylenediamine did the separation amount to 10-30%. 



The resolution of racemates by paper chromatography has been widely used 

 during the past years. Many attempts [27] to resolve racemic acids and amines on 

 the celluloses of paper and deacetylated chitin [28] have failed to give satisfactory 

 results. Only on paper treated with (+)-tartaric or (+)-camphorsulphonic acid, 

 at first using optically active solvents, has it been possible to separate the anti- 

 podes of /3-hydroxynaphthylbenzylaniine [29], phenylalanine [30] and tyrosine- 

 3-sulphomc acid. The separation occurs even without the use of optically active 

 solvents, which is explained by the asymmetric character of the adsorption on the 

 cellulose of the paper [31]. 



Many examples of the separation into antipodes of racemic amino acids and 

 sugars are now known and their number is steadily growing [32]. 



A method for the resolution of racemates of special theoretical interest has 

 recently been published. It is based on the selective spontaneous crystallization 

 of inclusion complexes, formed by the honeycomb-like spiral structure of a 

 complex-former, with insertion, into the spaces thus formed, of molecules of 

 the racemate to be resolved [33]. 



The adsorbent or complex-former may be optically active, racemic or inactive. 



