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Zeeb Road, Ann Arbor, Michigan 48106 8618759 Chandrasekaran, Appavu MICROBIAL AND HUMAN METABOLISM OF CARDIAC GLYCOSIDES The Ohio State University Ph.D. 1986 University Microfilms International 300 N. Zeeb Road, Ann Arbor, Ml 48106 Microbial And Human Metabolism of Cardiac Glycosides DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Appavu Chandrasekaran, M.S. •it it ★ ★ * The Ohio State University 1986 Dissertation Committee: Approved by Larry W. Robertson, Ph.D. Richard H. Reuning, Ph.D. Raymond W. Doskotch, Ph.D. Duane D. Miller, Ph.D. ^srry/fa. Robertson, Adviser Department of Medicinal Chemistry and Pharmacognosy DEDICATION To My Family - ii - ACKNOWLEDGEMENTS I wish to express my deep and sincere appreciation and gratitude to my adviser Dr. Larry W. Robertson for his guidance, encouragement, and support during the course of my graduate studies. I wish to extend my appreciation to Dr. Richard H. Reuning for his encouragement and valuable discussions. My thanks are also extended to Dr. Duane D. Miller for his interest and encouragement. 1 wish also to specifically thank Dr. C.E. Cottrell, Dr. Raymond W. Doskotch, and Mr. Jack Fowble for help in obtaining NMR spectra. The assistance of Dr. Alan G. Marshall, Mr. Ron E. Shomo and Mr. C.R. Weisenberger in obtaining MS data is also appreciated. I would like to thank Dr. Jack L. Beal for support and encourage­ ment during the course of my graduate program. I would like to express my thanks to my fellow graduate students and postdoctoral fellows, especially Tim Driscoll, Mohammed Elsheikh, Doug Geraets, James Hui, John Loper, Bob McClanahan and Raghu Nair, for their friendship, suggestions and assistance. I wish also to thank Ms. Carol A. Stewart for typing this thesis. Finally, I would like to gratefully acknowledge my loving wife, Thilagavathi, for her support, love and understanding. -iii- VITA June 17 , 1936*«« . « . Born - Munivalai, India June 1973 - June 1976. B.Sc. Botany, University of Madras, India June 1976 - Aug. 1978 M.Sc. Botany, University of Madras, India Jan. 1980 - Sep. 1981 M.S. Pharmacy, University of Houston, Houston, Texas Sep. 1981 - present Graduate Associate College of Pharmacy, The Ohio State University, Columbus, Ohio Publications: Robertson, L.W., Chandrasekaran, A., Reuning, R.H., Hui, J., Rawal, B.D.: "Reduction of Digoxin to 20R-Dihydrodigoxin by Cultures of Eubacterium lentum", Appl. Environ. Microbiol.,1986, in press. Shepard, T.A., Hui, J., Chandrasekaran, A., Sams, R.A., Reuning, R.H., Robertson, L.W., Caldwell, J.H., Donnerberg, R.L.: "Digoxin and Metabolites in Urine and Feces: A Fluorescence Derivatization HPLC Technique", J. Chromatogr. (Biomed. Appl.), 1986, in press. Major Field: Pharmacognosy -iv- TABLE OF CONTENTS Page DEDICATION...................................................... ii ACKNOWLEDGEMENTS ................................................ iii VITA ...............................................................iv LIST OF TABLES.................................................. xi LIST OF FIGURES.................................................. xiii LIST OF NONSTANDARD ABBREVIATIONS............... xvi GENERAL INTRODUCTION ............................................ 1 PART I .......................................................... .2 CHAPTER I. INTRODUCTION............................................ 3 1.1 History.......................................... 3 1.2 Sources of Cardiac Glycosides .................... 3 1.3 Chemical Structures and Structure Activity Relationships.................................... 7 1.3.1 Structure Activity Relationships: ........... 12 1.3.1.1 A-B-C-D ring system .................. 13 1.3.1.2 3-OH Group............................ 14 1.3.1.3 14-Hydroxy group ...................... 16 1.3.1.4 12 6-hydroxy group..................... 17 1.3.1.5 Lactone r i n g ............... 18 1.3.1.6 Side-chain at C 3 ........................ 19 1.3.1.7 Influence of other structural modifications ...................... 21 1.4 Therapeutic U s e s ................................ 22 1.5 Mechanism of Action.............................. 23 1.6 Metabolism of Digoxin and Digitoxin............... 24 1.7 Statement of the Problem........................ 35 -v- II. RESULTS AND DISCUSSION 38 2.1 Reduction of Digoxin to 20 R -Dihydrodigoxin . 38 2.1.1 Introduction....................... 38 2.1.2 Stereochemistry of digoxin reduction products. ................ 39 2.1.3 Hydrolysis of the sugar side chain.......... 40 2.1.4 Reduction of the sugar-hydrolyzed metabolites of digoxin..................... 40 2.1.5 Control experiments ...................... 45 2.1.6 Preparative-scale production of dihydro metabolites........................ 45 2.1.6.1 Mixed culture experiments, .......... 46 2.1.6.2 Variation of media and stationary versus shaken cultures............... 46 2.1.6.3 Concentration study ................ 47 2.1.6.4 Tlme-course study .................. 48 2.1.7 Isolation of the reduced metabolites. 48 2.1.8 Mass spectral evidence...................... 49 2.1.9 Preparation of dihydrodigoxigenin from dihydrodigoxin ........................ 58 2.1.10 CD and NMR spectroscopic evidence .... 58 2.1.11 Conclusion .............................. 61 2.2 Identification and Measurement of Digoxin and its metabolites........................... 62 2.2.1 Introduction.............................. 62 2.2.2 Identification of 20R-Dihydrodigoxin as the Major Reduced Metabolite ........ 66 2.3 Reductive inactivation of Digitoxin by cultures of Eubacterium lentum .......... 81 2.3.1 Introduction.............................. 81 2.3.2 Chromatographic (HPLC) identification of dihydrodigitoxin........................ 82 2.3.3 Hydrolysis of the sugar side chain.......... 82 2.3.4 Formation of reduced metabolites from DT2, DTI and DTO........................... 86 2.3.5 Control experiments......................... 88 2.3.6 Large-scale (mg) production................. 88 2.3.6.1 Mixed culture experiments....... 88 2.3.6.2 Concentration study............. 89 2.3.6.3 Time-course study .................. 89 2.3.7 Isolation of the m e t a b o l i t e s .............. 90 2.3.8 Mass spectral e v i d e n c e ....................90 2.3.9 Preparation of Dihydrodigitoxigenin from Dihydrodigitoxin .................. 98 2.3.10 Determination of the stereochemistry of dihydrodigitoxigenin................... 98 2.3.10.1 Conclusions .................... 105 - vi - III. EXPERIMENTAL ........................................ 106 3.1 Reduction of Digoxin to 20R-Dihydrodigoxin by cultures of Eubacterlum lentum........... 106 3.1.1 Chemicals and M e d i a .................... 106 3.1.2 Microorganisms ....................... 106 3.1.3 Instrumentation....................... 107 3.1.4 Pure E. lentum Culture Trans formations........................ 107 3.1.5 Fecal Samples.......................... 108 3.1.6 Extraction Procedures.................. 108 3.1.7 Derivatization........................ 109 3.1.8 Preparation for HPLC Chromatography. 109 3.1.9 H P L C .................................. 110 3.1.10 Standard Curves ...................... 110 3.1.11 Controls .............................. Ill 3.1.12 Preparative-Scale Production of Dihydro Metabolites ................ Ill 3.1.12.1 Mixed cultures .................. Ill 3.1.12.2 Variation of media .............. 112 3.1.12.3 Concentration study ............ 112 3.1.12.4 Time-course study .............. 113 3.1.12.5 General isolation procedures. 113 3.1.12.6 Isolation and purification of digoxin