Enantiomorphs, sweet

By 1938, one fact was clearly established. Sweet compounds, unlike salty and sour compounds, are found in all classes of chemical compounds, including such inorganic salts as beryllium ( glucinium ) and lead salts. They are also found among compounds of all molecular shapes and sizes, and stereochemical changes may result in a very dramatic change in the taste, as seen in the gustatory differences between enantiomorphs. 

It was with the sweet taste of enantiomorphs that we encountered the strongest criticism to our explanation of why sugars vary in their sweetness and also as to the identification of the saporous unit as an AH,B system in all sweet compounds. 

The d and L-sugars and amino acids are enantiomorphs and differ in absolute configuration about every asymmetric carbon atom. The pentose L-arabinose is structurally related to the sweet-tasting hexose, D-galactose, and, to recognize this, we predicted (2) that L-arabinose would probably taste sweet. 

Enzymatic hydrogenations generate optically pure isomers attempts to initiate such processes are made on metal-catalyzed hydrogenations. Asymmetric hydrogenation can fill the need for asymmetric compounds of which only one enantiomorph is active, e.g., amino acids such as L-lysine, 1 (indispensable in animal feeds), L-phenylalanine, 2 (a sweet peptide component), L-dopa 3 (a drug for Parkinsonism), are required in the L-form for human or animal consumption. Consequently, most of the examples investigated are related to the asymmetric hydrogenation of acrylic acid or cinnamic acid derivatives. 

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