In this contribution, we describe how the supramolecular synthon approach can be used for discovery of novel crystal forms and for enhancing the relevant preclinical properties of a low solubility antiepileptic drug, lamotrigine (6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine). Ten novel crystal forms are reported: lamotrigine methylparaben cocrystal form I (1:1) (1), lamotrigine methylparaben cocrystal form II (1:1) (2), lamotrigine nicotinamide cocrystal (1:1) (3), lamotrigine nicotinamide cocrystal monohydrate (1:1:1) (4), lamotrigine saccharin salt (1:1) (5), lamotrigine adipate salt (2:1) (6), lamotrigine malate salt (2:1) (7), lamotrigine nicotinate dimethanol solvate (1:1:2) (8), lamotrigine dimethanol solvate (1:2) (9), and lamotrigine ethanol monohydrate (1:1:1) (10). A selected set of the reported crystal forms were studied to determine their dissolution rate, solubility, and pharmacokinetic behavior. The solubilities were measured in aqueous media and in acidified aqueous media (pH = 1). It was observed that 5 and 2 exhibited the highest concentration in the aqueous media and acidified aqueous media, respectively. In the pharmacokinetic study, the serum concentration of lamotrigine, measured in Sprague−Dawley rats, reached the highest level after a single-dose oral administration of 5.

The use of labile As-S bond formation in the self-assembly of discrete supramolecular structures is extended. Macrocyclic structures of chemical formula As2L2Cl2 (H2L=alpha,alpha'-dimercapto-p-xylene) were prepared and characterized. Diastereomeric syn and anti isomers of these macrocycles were selectively crystallized and characterized in the solid state using single-crystal X-ray diffraction. Both the syn and anti macrocycles show close contacts between the arsenic(III) ions and the aromatic carbons, consistent with intramolecular arsenic-pi interactions. The dynamic behavior of the isomers in solution is also investigated. anti-As2L2Cl2.AsCl3 crystallizes in monoclinic space group P2(1)/c (No. 14) with a=10.6194(5) A, b=16.7780(9) A, c=8.5725(4) A, beta=100.6830(10) degrees, and Z=2. syn-As2L2Cl2 crystallizes in orthorhombic space group Pnma (No. 62) with a=10.8881(8) A, b=19.3511(14) A, c=9.9524(7) A, and Z=4.

Treatment of N-(2-mercaptoethyl)-1,8-naphthalimide (HL) with stoichiometric amounts of AsCl(3) and base affords AsL(2)Cl and AsL(3) complexes stabilized in part by secondary As...O bonding interactions.