The synthesis of the bovine pancreatic ribonuclease A (RNase A, EC 3.1.27.5) chromogenic substrate uridine-3'-(5-bromo-4-chloroindol-3-yl)-phosphate (U-3'-BCIP) is described. RNase A catalyzes the hydrolysis of U-3'-BCIP to release a halogenated indol-3-ol that undergoes rapid aerobic oxidation to the dark blue 5,5'-dibromo-4,4'-dichloroindigo. Preliminary kinetic studies indicate that this compound may have practical use for assaying RNase A activity both in vitro and in vivo, e.g. in screening bacterial colonies for RNase A produced by recombinant DNA methods.
The conformational behaviour of the peptide antibiotic leucinostatin A has been studied in solvents of different polarity using circular dichroism (CD) and infrared (i.r.) absorption. I.r. studies provided evidence of an intramolecularly hydrogen‐bonded structure in CDC3 while CD studies suggested a helical conformation in leucinostatin A in lipophilic solvents. The tetrapeptide Boc‐Aib‐Leu‐Leu‐Aib‐OMe, a fragment of leucinostatin A, was also studied both in solution and in solid state using X‐ray diffraction. The crystal structure shows that the peptide backbone folds into a right‐handed 310‐helical conformation stabilized by two intramolecular 4 → 1 hydrogen bonds. The spectroscopic analysis in solution is consistent with the conformation found in solid state. Crystal data: orthorhombic, P212121, a= 23.583, b= 15.791, c= 9.554 Å Z = 4; the final R and Rw are 0.090 and 0.126, respectively.
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