DESIGN AND SYNTHESIS OF SOME ARYLOXYARYL SEMICARBAZONES AND RELATED COMPOUNDS AS NOVEL ANTICONVULSANTS A Thesis Submitted to the College of Graduate Studies and Research in Partial fulfillment of the Requirements for the Degree of Doctor of Philosophy in Pharmacy BY Puthucode Ramanan Narayan Spring 1996 @ Copyright Puthucode Ramanan Narayan, 1996. All rights reserved. National Library Bibliothaue nationale du Canada Acquisitions and Acquisitions et Bibliographic Services sewices bibliographiques 395 Wellington Street 395. rue Wellington OttawaON KIAON4 Ottawa ON KIA ON4 Canada Canada Yarrfi vQtmrd&knw Our t% Norre rdfdrente The author has granted a non- L'auteur a accorde une licence non exclusive licence allowing the exclusive pernettant a la National Library of Canada to Bibliotheque nationale du Canada de reproduce, loan, distribute or sell reproduire, prster, distribuer ou copies of this thesis in microform, vendre des copies de cette these sous paper or electronic formats. la fome de microfiche/fihq de reproduction sur papier ou sur format eectronique. The author retains ownership of the L'auteur conserve la propriete du copyright in this thesis. Neither the droit d'auteur qui protege cette these. thesis nor substantial extracts fiom it Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent etre imprimes reproduced without the author's ou auh-ement reproduits sans son permission. autorisation. UNIVERSITY OF SASKATCHEWAN College of Graduate Studies and Research SUMMARY OF DISSERTATION Submitted in partial fulffflment of the requirements for the DEGREE OF DOCTOR OF PHILOSOPEW by Puthucode Ramanan Narayan College of Pharmacy and Nutrition University of Saskatchewan Spring 1996 Examining Committee: Dr. R.T. Card Dean's Designate, Chair College of Gradauate Studies & Research Dr. E. M. Hawes Chair of Advisory Committee College of Pharmacy and Nutrition Dr. J. R Dimmock Supervisor, College of Pharmacy and Nutrition Dr. J. W. Hubbard CoHege of Pharmacy and Nutrition Dr. J. D. Wood Department of Biochemistry Dr. J. M. Tuchek Department of Pharmacology External Examiner: Dr. C. R Clark School of Pharmacy Auburn University Alabama 36849-550 1 USA DESIGN AND SYNTHESIS OF SOME ARYLOXYARYL SEMICARBAZONES AND RELATED COMPOUNDS AS NOVEL ANICONWLSANTS Epilepsy is one of the most common neurological disorders affecting approximately 2% of the world's population. Unfortunately, currently available drugs are effenive in only 65% of the patients and their use may be associated with sigdicant side effects causing disability with considerable socioeconomic implications. Thus. there is an urgent need for new antiepileptic drugs with greater efficacy, specificity and lower toxicity. The development of new antiepileptic drugs remains a challenging problem. since both the prirnw pathologies of epilepsy and the precise mechanisms by which available anticonvulsants act are not well understood- Therefore. the search for new antiepileptic drugs continues to be an active area of investigation in medicinal chemistry. Previous studies revealed that a number of aryl sernicarbazones on oral administration to rats possessed signilicant anticonvulsant activity (ED5, figures in the 20-25 mgkg range) in the MES screen. In addition some of these compounds displayed good protection indices (PI viz. TDr&Dr, of appro-uirnately 25). Lf the aryl sernicarbazones displaying activity in the MES screen interact at a specific binding site. it is likely that the semicarbazono group and the aryl ring align at complementq areas on a macromolecular complex in vivo which have been referred to as the hydrogen bonding area and the aql binding site respectively (Fig. 1). Auxilianr Bindina Area Awl Bindina Site Hvdmsen bond in^ Area Fig. 1 Proposed binding site of aryl semicarbazoncs The principal aim of the study was to investigate the area around the postulated aryl binding site. which is shown in Fig. I as the ausiliaxy binding area with the main view of improving the potency. Ideally an ED5()of 1-3 mg/kg when administered orally to rats will be achieved. The biodata generated on these compounds may afford a clearer picture of the nature of the postulated binding site. A number of axyloxyaqd semicarbazones and related compounds WUE synthesized and evaluated for anticonvulsant activities. After intraperitoneal injection to mice, the Semicart,azones were examined in the MES , scPTZ and neurotoxicity screens. The resuits indicated that greater protection was obtained in the MES test than the scPrZ screen Quantitation of approximately one-third of the compounds revealed an average protection index of approximately 9. After oral administration to rats, a number of compounds displayed significant potencies in the MES screen (EDM of 1-5 mgkg) accompanied by very high protection indices. In fact over half the compounds had PI figures of greater than 100 and four were in excess of 200 and two compounds displayad protection &dices greater than 300. These compounds are ranked very high in terms of pure activity. A number of compounds displayed greater potencies and PI figures in the mouse intraperitoneal and rat oral screens than three clinically used drugs viz phenytoin, cubamazepine and valproate. Patent protection for these novel semicarbazones were made at the US Patent Oifice on June 7, 1995. The data generated fiom these studies supported a binding site hypothesis. Quantitative structure-activity relationships indicated a number of physicochemicaf parameters which contributed to activity in the MES screen X-ray crystallography and moiecular modeling of five compounds suggested the importance of certain interatomic distances and bond angles for activity in the mouse and rat MES screens. In presenting this thesis in partial fulfdment of the requirements for a postgraduate degree from the University of Saskatchewan, I agree that the libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor who supervised my thesis work or, in his absence, by the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Request for permission to copy or to make other use of material in this thesis in whole or part should be addressed to : Dean of the College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan, CANADA S7N SC9 TO PARENTS, MEMORY OF MOTHER-lN-LAW, WIFE SHREEDEVI AND DAUGEmR SHALINI ACKNOWLEDGMENTS There are many people to whom I owe a debt of gratitude for the help I received throughout the course of this project. First and foremost, I wish to sincerely thank Dr. J. R Dirnmock for his personal interest, guidance, and encouragement during the course of the research work and in the preparation of this thesis. I acknowledge the appropriate suggestions provided to me by the members of my advisory committee: Dr. E. M. Hawes, Dr. J. W. Hubbard, Dr. J. M. Tuchek and Dr. J. D. Wood. I would especially like to express my appreciation to Dr. S. N. Rao, Dr. J. M. Tuchek and Dr. V. Gopal for the time they devoted towards my academic and research endeavors. The rich facilities and the Eendly atmosphere that were bestowed on me by the College of Pharmacy and Nutrition, University of Saskatchewan are also acknowledged. I would like to thank Nordic Merrell Dow Research, Laval, PQ, Canada, for financial suppon of this project and Mr. J. P. Stables (NDlJ for generating most of the biological data. Appreciation is recorded to Dr. J. W. Quail, Dr. L. Prasad and Mrs. U. Pugazhenthi for assistance in the interpretation of the X-ray clystdographic data. My thanks are also due to C. Savithi, M. A. Saeed, (Department of Chemistry), A Lo, L M. Smith, C. Thomson (summer students), and M. Hetherington for their contributions to my research project. The timely help offered by K. G. Tischler, N. M. Kandepu, H. V. Raghuram, H. Jyothsna, V. Iowkin and V. Khanna are greatly appreciated. I also extend my thanks to all my colleagues for their cooperation throughout this work. Finally I would like to thank all my family members especially my wife Shreedevi and daughter Shalini for their love, patience and understanding during the long months of intense labor needed to complete this task. They provided the comfort and support necessary to sustain the human psyche that science never can grant. ABSTRACT Epilepsy is one of the most common neurological disorders affecting approximately 2% of the world's population. Unfortunately, currently available drugs aneffective in only 65% of the patients and their use may be associated with significant side effects causing disability with considerable socioeconomic implications. In addition, between 10 and 25 % of epileptic patients have chronic intractable seizures that are inadequately controlled with the currently available antiepileptic drugs. Thus, there is an urgent need for new antiepileptic drugs with greater efficacy, specificity and lower toxicity. The development of new antiepileptic drugs remains a challenging problem, since both the primary pathologies of epilepsy and the precise mechanisms by which available anticonvulsants act are not well understood. Therefore, the search for new antiepileptic drugs continues to be an active area of investigation in medicinal chemistry. Two major pharmacological screening tests used to evaluate compounds for anticonvulsant activities are the maximal electroshock screen (MES) and the subcutaneous pentylenetetrazol (scPTZ) screen. These tests are claimed to detect compounds possessing activity against generalized tonic-cIonic (grand mal) and generalized absence (petit mal) seizures. The structural requirements for activity in the MES screen have been stat& t; be the presence of a Iarge hydrophobic group which is in close proximity to at least two electron donor atoms.