Structure modification and biological activity of some griseofulvin derivatives.

Griseofulvin is an orally acting anti-fungal antibiotic with very limited water solubility. Five chemical modifications were made on the griseofulvin structure in order to evaluate these changes on the antifungal and water solubility properties. Antifungal activity was measured against Tricophyton mentagrophytes, T. rubrum, T. terrestre, and Microsporum canis. The oxime of griseofulvin was the most potent of the five compounds tested, but it was only of equal or less potency than griseofulvin. The somewhat increased water solubility of some of these compounds was offset by the lower anti-fungal potency of the structural modification.

Specificity and affinity of binding of phosphate-containing compounds to CheY protein.

1H- and 31P-n.m.r. have been used to study the interaction of the bacterial chemotaxis protein, CheY, with ATP and a variety of other phosphates in the presence and absence of bivalent metal ions. In the metal-bound conformation, CheY will bind nucleotide phosphates and phosphates in general, while in the metal-free conformation CheY loses its affinity for phosphates. In the presence of low concentrations of nitroxide-spin-labelled ATP (SL-ATP), specific proton resonances of metal-bound CheY are suppressed, indicating that ATP binds to a specific site on this metal-bound form of the protein. These studies also show that the same resonances are affected by the binding of SL-ATP and Mn2+, indicating that the phosphate- and metal-binding sites are close to each other and to Asp-57 (the site of phosphorylation in CheY). 1H- and 31P-n.m.r. studies using ATP, GTP, TTP, UTP, ADP, AMP and inorganic phosphates show that the binding is not specific for adenine, and does not involve the base directly, but is mediated primarily by the phosphate groups. Experiments with a phosphorylation mutant (Asp-13-->Asn) suggest that the observed phosphate binding and activation of CheY by phosphorylation may be related. Our results indicate that the conformational change and charge interactions brought about by the binding of a metal ion at the active site are required for CheY to interact with a phosphate. These studies also demonstrate the utility of spin-label-induced relaxation in conjunction with two-dimensional-n.m.r. measurements for exploring ligand-binding sites.

Hemoglobin S antigelation agents based on 5-bromotryptophan with potential for sickle cell anemia.

5-Bromotryptophan (5-BrTrp) is the most potent amino acid derivative reported in the literature to inhibit the gelation of hemoglobin S (from sickle cell anemia patients). Trp-Trp is also more potent than Trp as an antigelation agent. Therefore, we have prepared a series of dipeptides containing 5-BrTrp and evaluated the antigelation activity. 5-BrTrp-5-BrTrp is the most potent, i.e., 5.9 times the activity of Trp, followed by 5-BrTrp-Trp and then Trp-5-BrTrp. This improved antigelation potency for 5-BrTrp-5-BrTrp and 5-BrTrp-Trp is very significant and will be pursued further as lead compounds with potential for sickle cell anemia.