Hi thanks for your quick reply and concern. That centered OH- is an issue. I am afraid that if I halogenate the molecule, the uracyl group could end up modified. There is an easier way to get around it. The strain of cyanobacteria also produces a chemical variant of this toxin (see figure 4 ). I am also isolating this deoxy variant, which has very similar toxic effects on mammalian cells. I can use the deoxy variant instead of modifying the cylindrospermopsin. This way I will only have one OH- group to worry about. This toxin inhibits protein synthesis, so we believe it may bind with ribosomes or other proteins related to the translation process. I am not familiarized with pull down assays myself, but I am willing to try different polimers and linkers which might improve my chances. PS: Sorry for the double bond missing on the drawing, you were right.