Involved in the biosynthesis of the indolocarbazole antitumor agent rebeccamycin. Catalyzes the hydrogen peroxide-dependent dimerization of two L-tryptophan-derived molecules (imine form of indole 3-pyruvate (IPA)), to form dichlorochromopyrrolic acid (CPA), the precursor for the six-ring bisindolopyrrolocarbazole scaffold of the rebeccamycin. The hydrogen peroxide is provided together with iminoindolpropanoate by RebO. Due to the instability of indole 3-pyruvate (IPA), which is hydrolyzed in solution and exits in equilibrium with the predominant ketone form of IPA, the concerted functioning of the RebO/RebD system appears to prevent the buildup of significant amounts of IPA and its imine in solution, effectively shepherding the imine further down the biosynthetic chain. 2 3-(7-chloroindol-3-yl)-2-iminopropanoate + H2O2 = dichlorochromopyrrolate + H(+) + 2 H2O + NH4(+) 2 2-iminio-3-(indol-3-yl)propanoate + H2O2 = chromopyrrolate + H(+) + 2 H2O + NH4(+) 2 H2O2 = 2 H2O + O2 kcat is 64000 min(-1) for 2-imino-3-(indol-3-yl)propanoate (at pH 7.5). Homodimer. Belongs to the RebD family.