Crystal structures and conformational analysis of ochratoxin A and B: probing the chemical structure causing toxicity

Studies performed on two metabolites from Aspergillus ochraceus, ochratoxin A (1) and B (2), have yielded information related to the steric, conformational, and electronic considerations that could contribute to the different toxicities of these metabolites. The relative HCl-catalysed hydrolysis rates of the toxins are reversed compared with those observed in biological systems. This reversal of relative rate is ascribed to steric hindrance due to the chloro group in ochratoxin A (1). Single-crystal X-ray structural analyses, i.r., and high field n.m.r. analysis indicate no discernible difference in conformations.