Screening a natural product-based combinatorial library using FTICR mass spectrometry.

This manuscript reports the use of Fourier transform ion cyclotron resonance mass spectrometry to screen a combinatorially generated natural product-based library for binding affinity to bovine carbonic anhydrase II (bCAII). The fungal natural product 3-chloro-4-hydroxyphenylacetamide was the library template, with 11 secondary amide analogues of this template constituting the combinatorial library. 2-(3-Chloro-4-hydroxyphenyl)-N-(4-sulfamoylphenethyl)acetamide (compound 11) of this library was identified as a tight binding inhibitor of bCAII, by detection of a noncovalent complex corresponding to [bCAII+11] in the mass spectrum. A competitive bCAII enzyme binding assay validated the mass spectrometry screening result. The equilibrium dissociation constant (K(i)) for 11 was measured as 77.4 nM. Preliminary structure-activity investigations of the bioactive natural product analogue are also reported.