Helicity control in the preparation of chiral co-crystals from tryptamine and achiral carboxylic acids by pseudo-seeding

Chiral crystals of tryptamine and achiral carboxylic acids such as p-chloro benzoic acid, cinnamic acid, p-chlorocinnarnic acid and p-methylcinnamic ac id were prepared by crystallization from the solutions of both components. All the crystals belonged to typical chiral space group P2(1)2(1)2(1). The crystal chirality is generated through the formation of a unidirectional tw ofold helix between the two components through quaternary ammonium salt int eraction and hydrogen bonding in the lattice. This kind of spontaneous crys tallization necessarily gives crystals of both clockwise and counterclockwi se helicites. Here, pseudo-seeding based on utilizing these crystals as see d crystals was examined, resulting in successful helicity control in crysta llization from solutions of tryptamine and different carboxylic acids.