Solubility-isomerization relationship

Fig. 6. A highly idealized model for the plasma albumin molecule to account for the N-F transformation and its relationship to the titration anomaly, the cooperative detergent binding, and the altered solubility behavior of the low pH form. The model contains four folded amphipathic subunits, the hydrophobic surfaces being buried in the N form and exposed in the F form. Holes around the periphery of the molecule represent the 10 to 12 strong binding sites for detergent ions which are destroyed, upon isomerization, with the exposure of a large number of weaker sites. Reprinted with permission from Foster (1960). Copyright by Academic Press, Inc.

The stem, wood, and bark of Uncaria kawaJcamii contain the two isomeric alkaloids, uncarine-A and uncarine-B, C21H24N2O4 (30, 31), the highest proportion of alkaloids (1.48%) occurring in the bark (31). Uncarine-B has been identified with formosanine (28, 33), which was isolated earlier from Ourouparia formosana (21, 32). The chemical behavior of uncarine-A and formosanine is identical in all respects, and their relationship as stereoisomers is shown by their ready interconversion and equilibration, which frequently hinders the separation and purification of individual isomers. Thus, uncarine-A in hot dilute acetic acid yields formosanine, and the reverse transformation can be achieved by heating formosanine with ether, until it has all been isomerized into the more soluble uncarine-A. Some formosanine is even obtained when uncarine-A is recovered from its hydrochloride, or from the hydrochloride of the related amino acid, by methylation with diazomethane (59). 

The hexahydroxycyclohexanes have long been of particular interest to those concerned with the carbohydrates. Originally this interest arose from the fact that they are isomeric with the hexoses and resemble the sugars in water solubility and sweetness it has been sustained by their unique properties, their stereochemical relationships and, finally, by the tantalizing question of their significance in nature. The present review will deal chiefly with the chemistry and configurations of the hexahydroxycyclohexanes or inositols, as they are frequently called, and will touch on certain other closely related polyhydroxycarbocyclic substances. The convenient term cyclitol has come to denote the type of compound that will be considered herein. 

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