Free long-chain bases

Wakita, H., Nishimura, K., and Takigawa, M., Composition of free long-chain (sphingoid) bases in stratum corneum of normal and pathologic human skin conditions, J. Invest. Dermatol., 99, 617,... 

The structures of long-chain bases can best be determined by mass spectrometry (Karlsson, 1970b). The dinitrophenylamines with their free hydroxyl groups methylated give characteristic fragmentation patterns for determination of their molecular weights and the primary structure of the base. Double-bond positions can be found if they are first hydroxylated and derivatized to TMS (tri-methylsilyl) ethers. Mass spectra can also be obtained (after GLC) of the A -acetyl, O-TMS ether derivatives of the base (Polito et aL, 1969). trans-Douhlc bonds can be identified by infrared absorption spectroscopy. 

Several methods have been described for localizing carbon double bond positions in long-chain bases, depending on the identification of their oxidation products. In the case of oxidation with MnOj/IO (Sweeley and Moscatelli, 1959 Sambasivarao and McCluer, 1964 Ramachandran et ah, 1968 Polito et al., 1968) or oxidative ozon-olysis (M rtensson, 1964) fatty acids are obtained. Treatment with OSO4 / 104 or reductive ozonolysis yield free aldehydes, which can be analyzed directly or as 1,3-dioxolane derivatives by gas-liquid chromatography (Panganamala et al., 1969 Venkata Rao et al., 1967). 

Lipolysed milk fat was one of the first flavours produced with the help of enzymes. The original process was based on the controlled lipase-catalysed hydrolysis of cream [18]. For instance, Mucor miehei lipase possesses a high selectivity towards flavour-active short-chain fatty acids. Additionally, lipases that prefer long-chain fatty acids or lipases without particular preferences can be found. The free fatty acids produced can be isolated by steam distillation and further purified. Thus, it is possible to obtain pure short-chain fatty acids like butanoic, hexanoic, octanoic and decanoic acid. 

FIGURE 6.7 Cumulative lymphatic transport of halofantrine after oral administration in long-chain, Ci8 ( ), medium-chain, Cs-io (o), and short-chain, C4 (A) triglyceride lipid-based formulations, and a lipid-free (V) formulation. (From Caliph, S.M., et al., J. Pharm. Sci., 89, 1073, 2000. With permission.)... 

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