Sugar isothiocyanates amino acids

For those without native fluorescence, two common approaches have been employed, namely, derivatization and indirect fluorescence. Derivatizing agents should be pure, low fluorescent, and stable, as well as react quickly and uniquely with the analytes and, thus, formed compounds should be strongly fluorescent and stable. These include dansyl chloride, fluorescamine, 4-clair-7-nitro-benz-2-oxa-l,3-diazole (NBD), o-phthaldialdehyde (OPA), fluorescein isothiocyanate (FITC), and naphthalene-2,3-dicarboxaldehyde (NDA), which have been used for the analyses of amino acids, peptides, proteins, thiols, and sugars with LOD in 1-100 nM range. Compared to LINF, approaches based on derivatization provide the advantages of relatively low cost and versatility in instrumentation, but they may suffer from contamination and loss of temporal information. 

The reaction of sugar isothiocyanates with aminosugars described above has also been studied with 1-amino (alkyl and arylamino)-l-deoxy-D-fructose 143 (Scheme 32). Thus, treatment of different 0-acylated sugar isoth-iocyanates with D-fructosamines 143 gave M-glycosyl-5-hydroxy-5-tetritolyl-imidazolidine-2-thiones 144 as pairs of diastereomers in almost quantitative yield [ 152]. The reaction times were shorter (15-20 min) for fructosamine or its M-methyl derivatives than in the cases of N-aryl derivatives (8-24 h). Acid-catalyzed dehydration of 144 with ethanolic TFA at rt led to 147 in 65-77% yield. These compounds can be considered simultaneously as M-nucleosides and acyclic C-nucleosides of imidazoline-2-thiones. 

Another main subject of research of Garcia Gonzalez, with the collaboration of J. Femandez-Bolanos, was the reaction of amino sugars with isothiocyanic acid derivatives. 2-Amino-2-deoxy-D-glucose hydrochloride and potassium thiocyanate were shown to give rise to 4-(D-arabino-tetritol-l-... 

Thioamides can serve as surrogates for isothiocyanates in the Marckwald synthesis. For example, reaction of a-amino acetals 1278 with thioamides 1277 in the presence of HgClz affords amidine intermediates, which cyclize to form imidazoles under acidic conditions. This method has been applied to synthesize a variety of sugar imidazoles (Scheme 324) <2005HCA10, 2004HCA3035, 2004HCA719, 2000TA435>. 

Deoxy-2-thioureido-sugars, e.g. 53 (R=Bz or CO2EO could be synthesized by direct condensation of amino-sugars with benzoyl or ethoxycarbonyl isothiocyanate, whereas similar reactions with aryl or alkyl isothiocyanates led to alditol-1-yl substituted heterocycles, e.g. 54 by way of 53 (R=Ph or Me). These monocyclic products further cyclize in dilute acetic acid to give 55... 

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