Design and pharmacological activity of glycinamide and N-methoxy amide derivatives of analogs and constitutional isomers of valproic acid Neta Pessah a , Boris Yagen a, b , Naama Hen a , Jakob A. Shimshoni a , Bogdan Wlodarczyk c , Richard H. Finnell c , Meir Bialer a, b, ⁎ a Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel b The David R. Bloom Centre for Pharmacy, The Hebrew University of Jerusalem, Jerusalem, Israel c Center for Environmental and Genetic Medicine, Institute of Biosciences and Technology, Texas A&M Health Science Center, Texas A&M University, Houston, TX, USA abstract article info Article history: Received 21 July 2011 Revised 22 August 2011 Accepted 23 August 2011 Available online 29 September 2011 Keywords: Valproic acid isomers and analogues Maximal electroshock seizure test Subcutaneous metrazol seizure test 6-Hz psychomotor seizure test Glycinamide conjugates N-methoxy derivatives A series of glycinamide conjugates and N-methoxy amide derivatives of valproic acid (VPA) analogs and con- stitutional isomers were synthesized and evaluated for anticonvulsant activity. Of all compounds synthesized and tested, only N-methoxy-valnoctamide (N-methoxy-VCD) possessed better activity than VPA in the fol- lowing anticonvulsant tests: maximal electroshock, subcutaneous metrazol, and 6-Hz (32-mA) seizure tests. In mice, the ED 50 values of N-methoxy-VCD were 142 mg/kg (maximal electroshock test), 70 mg/kg (subcutaneous metrazol test), and 35 mg/kg (6-Hz test), and its neurotoxicity TD 50 was 118 mg/kg. In rats, the ED 50 of N-methoxy-VCD in the subcutaneous metrazol test was 36 mg/kg and its protective index (PI=TD 50 /ED 50 ) was N 5.5. In the rat pilocarpine-induced status epilepticus model, N-methoxy-VCD demon- strated full protection at 200 mg/kg, without any neurotoxicity. N-Methoxy-VCD was tested for its ability to induce teratogenicity in a mouse strain susceptible to VPA-induced teratogenicity and was found to be non- teratogenic, although it caused some resorptions. Nevertheless, a safety margin was still maintained be- tween the ED 50 values of N-methoxy-VCD in the mouse subcutaneous metrazol test and the doses that caused the resorptions. On the basis of these results, N-methoxy-VCD is a good candidate for further eval- uation as a new anticonvulsant and central nervous system drug. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Valproic acid (VPA) (1, Fig. 1), a major antiepileptic drug (AED), is used for the treatment of various types of epileptic seizures [1–3]. Yet VPA is the least potent AED as reflected by its higher ED 50 and higher doses compared with other AEDs [4]. In addition, its clinical use is limited because of two severe side effects: teratogenicity and hepato- toxicity [5, 6]. Consequently, there is a substantial need for the devel- opment of new second-generation drugs to VPA that preserve its broad-spectrum efficacy at lower doses and lack hepatotoxicity and teratogenicity [5–12]. Both teratogenicity and hepatotoxicity are related to structure, although, unlike teratogenicity, hepatotoxicity results from a minor metabolite(s) of VPA with a terminal double bond (e.g., 4-ene-VPA) [13]. Following extensive structure–activity relationship (SAR) studies in mouse strains prone to VPA-associated teratogenicity, it has been found that an analog of VPA is likely to be teratogenic if it contains tertiary carbon bound to a carboxylic group, a hydrogen atom, and two alky chains [8, 14, 15]. Forming a VPA CoA ester is the first step in the formation of a VPA hepatotoxic metabo- lite(s). Therefore, a free carboxylic group is mandatory for VPA hepa- totoxicity [16]. Valpromide (VPD) (2, Fig. 1), the corresponding amide of VPA, is 4–10 times more potent than VPA in anticonvulsant animal (rodent) models and is nonteratogenic (mouse). VPD has been clinically used in Europe since the 1970s as an antiepileptic and antipsychotic agent [17]. Nevertheless, VPD's lack of teratogenicity and its better potency (compared with VPA) in animal models has no clinical impli- cations, because in humans, VPD is rapidly and presystemically metabolized to VPA and thus acts as a VPA prodrug [17]. Various amide derivatives of VPA, other than VPD, have been syn- thesized and evaluated in our laboratory and found to possess potent anticonvulsant activity in animal models with minimal metabolism to their corresponding acids [18–20]. Glycine is a neuroinhibitory amino acid and, when co-administered with other AEDs, demonstrated improved anticonvulsant potency in rats as a result of the synergism between the AED and glycine [21– 23]. Therefore, it was hypothesized that conjugation of VPA to inhibi- tory neurotransmitters such as glycine, taurine, and GABA would pro- duce potent anticonvulsants. Instead, it resulted in nonactive compounds [20]. However, conjugation of VPA to the corresponding amides of glycine and taurine led to valproylglycinamide (VGD) (3, Epilepsy & Behavior 22 (2011) 461–468 ⁎ Corresponding author at: Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, POB 12065 Ein Karem, Jerusalem 91120, Israel. Fax: + 972 2 6757246. E-mail address: bialer@md.huji.ac.il (M. Bialer). 1525-5050/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.yebeh.2011.08.026 Contents lists available at SciVerse ScienceDirect Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh