A Cl-amidine derivative with greater cellular potency against PAD4 activity (EC50 = 8.8 µM, vs. >200 µM for Cl-amidine) and a significantly longer in vivo half-life (1.75 h, vs. ~15 min for Cl-amidine); effective in vivo, improving endothelial function while downregulating the expression of type I interferon-regulated genes in MRL/lpr mice.