Figure 2.

Covalent binding of leptomycin B to N-acetyl-l-cysteine methyl ester and a peptide containing a cysteine. (A) Chemical structure of an LMB complex with N-acetyl-l-cysteine methyl ester and the chemical shifts of ¹H NMR. An adduct generated in the mixture containing LMB and N-acetyl-l-cysteine methyl ester was purified by HPLC, and the structure was determined by ¹H NMR and correlated spectroscopy. The chemical shifts are presented with the structure. (B) An addition reaction with a peptide containing a cysteine residue. An 18-aa peptide corresponding to hCRM1 residues 513–530 that contains Cys-528 was incubated with LMB for 24 h at 37°C and analyzed by matrix-assisted laser desorption ionization–TOF MS. A peak of 2,275.9 Da may be a product of the reaction between the peptide and α-cyano-4-hydroxycinnamic acid (αCHCA) used as the matrix. Calculated molecular mass (Da) is 540 for LMB, 2,104.54 for the peptide, and 189.04 for αCHCA.