Arginine-containing cyclodipeptide synthase; part of the cluster that mediates the biosynthesis of a highly modified cyclo-arginine-aspartate dipeptide (cRD). Within the pathway, pthA acts as the scaffold-generating enzyme and is responsible for formation of the cyclo-Arg-Asp diketopiperazine (cRW) from L-arginyl-tRNA(Arg) + L-aspartyl-tRNA(Asp). Additional enzymes from the cluster then further modify the cyclo-Arg-Asp diketopiperazine (cRW) scaffold (Probable)