For the synthesis of these vaccine candidates we have used different synthetic strategies , including the maleimide-thiol chemistry . In the latter, we used BMPS (N-(β-maleimidopropyloxy)succinimide ester), a crosslinker reagent that have been used previously in the synthesis of effective human conjugate vaccines against H. influenzae type B , shiguellosis , and more recently against SARS-CoV-2 .