form screening of drugs. This approach will lead to discover crystal forms including, but not limited to, salts, hydrates, solvates, and, more recently, co-crystals (9).
Pharmaceutical co-crystals are defined as multiple component crystals in which at least one component is molecular and a solid at room temperature (the co-former) and forms a supramolecular synthon with a molecular or ionic API (10) Numerous APIs that exhibit undesirable solubility or stability and possess multiple hydrogen-bonding sites have been (or potentially can be) studied in the context of co-crystallization. One of such potential APIs was identified to be Aceclofenac and is of interest for co- crystallization. Aceclofenac is a BCS class II drug with a pKa of 4.7. It has the capability of forming both the salt and co-crystal and it is a novel NSAID (11).
Chemically Aceclofenac has a carboxylic acid functional group and two chlorine atoms. The design strategy I of this molecule is to exploit the robust carboxylic-acid-amide heterosynthon and amide-chlorine atom heterosynthon when primary
amide containing Nicotinamide is used as co-
former while II strategy is to exploit the carboxylic acid dimer with exofunctional which acts as either a hydrogen bond donor or acceptor. So this chosen API renders itself to be amenable for the synthesis of co-crystals.
Nicotinamide is a GRAS status co-crystallizing compound. It is a primary amide with two
hydrogen bond donors (NH2) and an acceptor (C=O), demonstrate a remarkable ability to form hydrogen bonds for the formation of an intermolecular drug molecule: co-crystal former synthon. A second hydrogen bond acceptor is the lone pair on the N atom of the pyridine ring (12). This makes the molecule very versatile for a variety of hydrogen bonded interactions which makes Nicotinamide to be excipient of choice