Medicinal Chemistry, 2011, 7, 9-17 9 1573-4064/11 $58.00+.00 © 2011 Bentham Science Publishers Ltd. N-Valproyl-L-Tryptophan for CNS-Targeting: Synthesis, Characterization and Efficacy In Vitro Studies of a New Potential Antiepileptic Drug Viviana De Caro a, *, Giulia Giandalia a , Maria Gabriella Siragusa a , Liliana Lamartina a , Simonetta Friscia b , Pierangelo Sardo b , Fabio Carletti b , Valerio Rizzo b , Giuseppe Ferraro b and Libero Italo Giannola a a Dipartimento di Chimica e Tecnologie Farmaceutiche, Università degli Studi di Palermo, via Archirafi 32, 90123 Pa- lermo, Italy b Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche, Università degli Studi di Palermo, Via del Vespro 129, 90127 Palermo, Italy Abstract: A new aminoacidic derivative of valproic acid (VPA) has been synthesized and characterized by analytical and spectral data. The rationale for the preparation of such potential antiepileptic agent is based on the observation that chemi- cal combination of the anticonvulsant pharmacophore, VPA with essential aminoacids could afford more effective and less toxic actives. The synthesis, characterization, physico-chemical parameters functional for crossing Blood Brain Bar- rier of N-valproyl-L-tryptophan (4) are reported. The Log D pH7.4 (0.3) indicates that (4) is adequate to cross biological membranes. Its chemical and enzymatic stability were assessed. The experiments indicate high stability of compound (4) at pH conditions of physiological fluids. Moreover, both in plasma and in cerebral enzymatic environments compound (4) doesn’t undergo cleavage after 24 h. The anticonvulsant activity of the new compound was assessed against epileptic burst discharges evoked in vitro in rat hippocampal slices (Seizure like events - SLEs) and compared with that of the widely used VPA. Compound (4), even at the lower tested concentration, when compared to VPA, showed an improved protective effect against hippocampal sei- zures. The collected data suggest that compound (4) could be considered a very valuable candidate for subsequent in vivo evaluation as new potential antiepileptic drug. Keywords: Aminoacidic derivative, antiepileptic drug, CNS-targeting, enzymatic stability, seizure like events model, valproic acid. 1. INTRODUCTION Epilepsy, characterized by recurrent seizure attacks, is one of the most common neurological conditions, occurring in about 1% of the global population [1]. The main drawback related to epilepsy therapy is associ- ated with the fact that antiepileptic drugs (AEDs) fail to con- trol seizures in 20-25% of patients [2-4]. During the last decade, new AEDs that offer appreciable advantages in terms of favourable pharmacokinetics, im- proved tolerability and lower potential for drug interactions have been introduced [5-7]. The availability of both old and new AEDs with various activity spectra and different toler- ability profiles enables clinicians to better tailor drug choice to the characteristics of the individual patient. The new AEDs currently in development can be divided into two categories: I) drugs with completely new chemical structures such as lacosamide, retigabine, rufinamide and talampanel; II) drugs that are derivatives or analogues of existing AEDs that can be regarded as second-generation or follow-up compounds of established AEDs. *Address correspondence to this author at the Dipartimento di Chimica e Tecnologie Farmaceutiche, Università degli Studi di Palermo, via Archirafi 32, 90123 Palermo, Italy; Tel: +39 091 23891926; Fax: +39 091 23891962; E-mail: vdecaro@unipa.it Valproic acid (VPA), as sodium valproate, is currently marketed in over 100 countries and is well established as a first-line and widely used antiepileptic agent, with a very broad spectrum of activity against both generalized and par- tial seizures in adults and children. It is effective against ab- sences, myoclonic and generalized tonic-clonic seizures. Moreover, the drug is useful in the treatment of partial sei- zures, with or without secondary generalization [8, 9]. In spite of the broad spectrum of antiepileptic activity in some cases clinical use of VPA is restricted by its pharma- cokinetic and two rare but life-threatening side effects, i.e., hepatotoxicity and teratogenicity. VPA, owing to its latency time, has lower efficacy than the other antiepileptic drugs in acute treatments but it has the same efficacy in the chronic application. The delay of the antiepileptic efficacy of VPA has been attributed to metabolites of VPA [10, 11], to the influence of the blood brain barrier [12], or to long lasting binding of VPA to membranes [13]. Although VPA-induced hepatotoxicity is associated with the formation of metabolite(s) with a terminal double bond, VPA-induced teratogenicity is caused by the parent com- pound [14]. In the last decade some derivatives or analogues of VPA have been synthesized and tested in order to obtain new