Probe Cipro P1 was synthesized using substitution conditions with Ciprofloxacin and the literature known iodo-derivative of the minimalist photo-crosslinker (Scheme S1A). The corresponding Levofloxacin probe Levo P1 was synthesized starting from Levofloxacin Q-acid. After nucleophilic aromatic substitution to install the piperazine moiety, the minimalist photocrosslinker was appended accordingly (Scheme S1B). Amide coupling of the branched photoaffinity handle developed by Conway et al. to N-Boc-protected Ciprofloxacin and subsequent deprotection afforded Cipro P2 (Scheme S2A). Similar amide coupling conditions starting with Levofloxacin afforded Levo P2 (Scheme S2B).