| Assigning absolute configuration of molecules continues to be a major problem. Contradictory results have come from two of the most known methods, the exciton coupling circular dichroism (ECCD) method and the Mosher ester NMR analysis, for the configuration of C2 of Chromomycin A3 (CRA3). We have established the absolute stereochemistry of the key structural motif of CRA3 by using a combination of molecular modeling, solution 1H NMR, and X-ray crystallography. Our results explain why it is difficult to assign stereochemistry based on solution methods alone and suggest that a comparison of calculated and experimental optical rotatory dispersion (ORD) data provides the most straightforward way to assign the absolute configuration.; While a number of model systems have been designed for the study of polyvalent interaction, most of them focus on enhancement in binding avidities by carbohydrate clustering. We have designed a new model system, which allows for investigations of both kinetic details and thermodynamic effects of a polyvalent binding process. Using a glycosylated heptameric ion channel derived from the alpha-hemolysin pore, both the rate and binding constants for the interaction between Bauhinia purpurea (BP) lectin and the natural ligand disaccharide were measured. This system also provides a method to explore the effects of systematic changes in linker length and structure in polyvalent binding and will form a basis for construction of stochastic biosensors which can be used for detecting toxins, viruses, bacteria, and whole cells.; beta-Hydroxy amino acids are an important class of compounds ubiquitously occurring in nature. Due to their importance as building blocks of many bioactive natural products, an efficient synthetic route to this class of compounds is critical for both biological and chemical studies. We have synthesized requisite beta-hydroxy-tyrosine derivatives using an Evans asymmetric aldol condensation procedure for research directed towards construction of a new hybrid antibiotic and elucidation of the role of an enzyme NovJ/K in novobiosin biosynthesis. Also described herein is our exploration of the possibility of accessing beta-hydroxy amino acids by direct oxidation at the benzylic position of tyrosine. |
