4-imidazolidinehexanamide, N-[6-[[2-[(2-iodoacetyl)amino]ethyl]amino]-6-oxohexyl]-5-methyl-2-oxo-, (4R,5S)- DSB-X(TM)biotin C2-iodoacetamide desthiobiotin-X C2-iodoacetamide