Glycosides derivatization procedures

Potentially tautomeric pyrimidines and purines are /V-alkylated under two-phase conditions, using tetra-n-butylammonium bromide or Aliquat as the catalyst [75-77], Alkylation of, for example, uracil, thiamine, and cytosine yield the 1-mono-and 1,3-dialkylated derivatives [77-81]. Theobromine and other xanthines are alkylated at N1 and/or at N3, but adenine is preferentially alkylated at N9 (70-80%), with smaller amounts of the N3-alkylated derivative (20-25%), under the basic two-phase conditions [76]. These observations should be compared with the preferential alkylation at N3 under neutral conditions. The procedure is of importance in the derivatization of nucleic acids and it has been developed for the /V-alkylation of nucleosides and nucleotides using haloalkanes or trialkyl phosphates in the presence of tetra-n-butylammonium fluoride [80], Under analogous conditions, pyrimidine nucleosides are O-acylated [79]. The catalysed alkylation reactions have been extended to the glycosidation of pyrrolo[2,3-r/]pyrimidines, pyrrolo[3,2-c]pyridines, and pyrazolo[3,4-r/]pyrimidines (e.g. Scheme 5.20) [e.g. 82-88] as a route to potentially biologically active azapurine analogues. 

Gas-liquid chromatography (GLC) has notTeen employed for the analysis of flavanone glycosides because they are non-volatile and thermally unstable. One GLC method (28) has been developed for the analysis of the flavanone aglycones. However, the method is extremely time consuming in that the samples must be extracted, hydrolyzed and derivatized before analysis. Furthermore, the procedure cannot distinguish between bitter and nonbitter flavonoids. 

Nachtmann, F., Spitzy, H., and Frei, R.W., Rapid and sensitive high-resolution procedure for digitalis glycoside analysis by derivatization liquid chromatography, J. Chromatogr., 122, 293, 1976. 

Variously derivatized 2-deoxy- and 2,5-dideoxy-streptamines have been synthesized 2,5-dideoxystreptamine was prepared from kanamycin by a simple procedure, and 5 0-(2,3-dideoxy-a-D-e 7r/iro-hexopyranosyl)-2-deoxy-strepta-mine dihydrochloride was obtained by glycosidation of a 2-deoxystreptamine derivative with tri-O-acetyl-D-glucal and hydrogenation. " The preparation of a 5-aminocyclohexanetetrol from kanamycin A is mentioned in Chapter 18. 

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