Synthesis of Reduced Metabolites of Isoflavonoids, and Their Enantiomeric Forms
Total Page：16
File Type：pdf, Size：1020Kb
Synthesis of Reduced Metabolites of Isoflavonoids, and their Enantiomeric Forms Tuija Jokela Laboratory of Organic Chemistry Department of Chemistry Faculty of Science University of Helsinki Finland Academic Dissertation To be presented with the permission of the Faculty of Science of the University of Helsinki for public examination in Auditorium A110 in the Department of Chemistry, November 26th, at 12 o’clock. Helsinki 2011 Supervisor Professor Kristiina Wähälä Laboratory of Organic Chemistry Department of Chemistry University of Helsinki Finland Reviewers Professor Harri Lönnberg Laboratory of Organic Chemistry Department of Chemistry University of Turku Finland Professor Victor A. P. de Freitas Laboratory of Organic Chemistry Department of Chemistry University of Porto Portugal Opponent Professor Michael Orfanopoulos Department of Chemistry University of Crete Greece ISBN 978-952-10-7328-1 (paperback) ISBN 978-952-10-7329-8 (PDF) http://ethesis.helsinki.fi Helsinki University Printing House Helsinki 2011 ABSTRACT Isoflavonoids are naturally occurring plant derived biochemicals, which act as phytoalexins. Isoflavonoids are of interest due to their estrogenic and other potential physiological properties, particularly in mammals that typically consume isoflavonoid rich nutrients such as soy and red clover. The literature review of this thesis mainly focuses on the reduced metabolites of hydroxy and/or methoxy substituted isoflavones with four groups: isoflavan-4-ols, isoflav-3-enes, isoflavans and -methyldeoxybenzoins (1,2-diarylpropan-1-ones), which are all reduced metabolites of food derived isoflavones in mammals. Related isoflavan-4-ones are briefly discussed. Results of an extensive survey of the literature concerning the synthesis of polyhydroxy- or methoxysubstituted isoflavonoids and especially asymmetric approaches are discussed. The experimental section describes new synthetic methods to prepare polyphenolic reduced isoflavonoid structures such as isoflav-3-enes, isoflavan-4-ones, cis- and trans-isoflavan-4-ols, 1,2-diarylpropan-1-ones and isoflavans by various hydride reagents and hydrogenations. The specific reactivity differences of various hydride reagents toward isoflavonoids are discussed. The first enantioselective synthesis of natural (S)-(-)-equol and the opposite enantiomer (R)-(+)-equol is also described by the asymmetric iridium PHOX catalysed hydrogenation of isoflav-3-enes. Both of these equol enantiomers are found to possess biological activity in mammals due to estrogen receptor binding activity. The natural enantiomer prefers estrogen receptor and the R-enantiomer prefers the estrogen receptor . Also the precursor, isoflav-3-ene, is found to possess positive biological effects on mammals. In connection with the synthetic work, the (S)-(-)- equol was discovered from serum of ewes after isoflavone rich red clover feeding. The chiral HPLC method was developed to identify natural equol enantiomer for the first time in this species. The first synthesis of natural isoflavonoid (R)-(-)-angolensin and its enantiomer (S)- (+)-angolensin is desribed by the use of recyclable chiral auxiliaries (chiral pseudoephedrines). The method offers a general approach also to other natural polyphenolic 1,2-diarylpropan-1-ones and to further study isoflavonoid metabolism in human and other mammals. The absolute configurations of these new chiral isoflavonoid metabolites were determined by X-ray spectroscopy. Also thorough NMR and MS analysis of synthesised structures are presented. ACKNOWLEDGEMENTS This study was carried out in the Laboratory of Organic Chemistry, Department of Chemistry, University of Helsinki. Funding from the Emil Aaltonen Foundation, The Graduate School of Bioorganic Chemistry, the Chancellor of the University of Helsinki and the University of Helsinki Research Fund are gratefully acknowledged. I wish to offer my sincere thanks to a number of people, for a great range of support. My supervisor, professor Kristiina Wähälä, introduced me to the field of isoflavonoid chemistry and gave her continuous support, encouragement, advice and confidence during the entire project. Also, Professor Emeritus Tapio Hase, who accepted me as a graduate student in his laboratory, offered his invaluable advice on numerous chemical problems. Both have placed the research facilities of the laboratory at my disposal. Dr. Auli Salakka provided pleasant cooperation concerning isoflavonoid synthesis research. Professor Hannu Saloniemi, Dr. Juhani Taponen, Mrs. Eeva Mustonen, and Mr. Ilkka Saastamoinen offered fruitful collaboration in our multidisciplinary research concerning isoflavonoids and animal health. Dr. Johanna Lampe and other coworkers contributed to the isoflavonoid metabolism study, and Professor Ian Rowland and coworkers participated in our multidisciplinary research project. Dr. Kalle Nättinen performed X-ray measurements, and did analysis of diiodo-(S)- equol, chiral PHOX-ligand and catalyst. Dr. Cristine Cardin performed the X-ray analysis of (R)-angolensin. Professor Kalevi Pihlaja and his group collaborated on the computational NMR. The personnel at the Laboratory of Organic Chemistry always provided me with advice whenever I needed it. Dr. Jorma Matikainen assisted me greatly with HRMS measurements and taught me how to measure LRMS spectra. Mr. Seppo Kaltia and Dr. Markku Mesilaakso introduced me to NMR measurements. I also thank all of the former and present members of our Phyto-Syn research group whom are gratefully acknowledged. Special thanks go to Eija, Barbara and Sari for being such good friends both on and off duty. I also want to thank the “unofficial” Phyto-Syn member Nina for sharing the interest in higher education teaching and our ECTN cooperation. Antti and Satu-Maarit gave valuable input on isoflavonoid metabolism research and provided pleasant companionship at the Soy Conference in San Diego. Special thanks go to Kauko for maintaining a full service chemical warehouse and Matti Keinänen for technical support especially concerning hydrogenation equipment. Professor Harri Lönnberg and Professor Victor A. P. de Freitas have kindly reviewed the manuscript of the thesis and gave extremely helpful comments, and Dr. Jennifer Rowland revised the language of the manuscript. My present supervisors at Fermion, Arne and Lefa, have provided outstanding encouragement and given me the study leave to finish this manuscript. Also, other colleagues at Fermion have created an inspiring atmosphere. My sincerest thanks go to my parents for their unconditional love, support and trust in every aspect of my life. I’m especially grateful to your gentle caretaking of the boys. I would also like to thank Aino and Aukki for your kind support. I am especially grateful to my dear brother, who always kept the positive thinking no matter what. Finally, I would like to thank my Supermen, Mika, Roope and Lauri, for your love and support. I am most sincerely grateful for your endless patience and understanding during my late nights in our basement finishing up this manuscript. Vantaa, October 2011 Tuija Jokela CONTENT ABSTRACT 2 ACKNOWLEDGEMENTS 3 LIST OF ORIGINAL PUBLICATIONS 6 LIST OF ABBREVIATIONS 7 1. INTRODUCTION 9 1.1. Isoflavonoid sources in nutrition, mammalian metabolism and biological activities 11 1.2. Synthesis of isoflavonoid metabolites 1.2.2 Synthesis of isoflav-3-enes and isoflav-2-enes 18 1.2.2.1 2-O-Substituted or 2-N-substituted isoflav-3-enes 24 1.2.3 Synthesis of isoflavans 26 1.2.3.1 Catalytic hydrogenation of isoflavones 27 1.2.3.2 Multistep total syntheses 31 1.2.3.3 Synthesis of enantiopure isoflavans 35 1.2.4 Synthesis of -methyldeoxybenzoins 41 1.2.4.1 Synthesis of racemic -methyldeoxybenzoins (1,2-diarylpropan-1-ones) 41 1.2.4.2 Asymmetric synthesis of 1,2-diarylpropan-1-ones 45 2. AIMS OF THE STUDY 48 3. RESULTS AND DISCUSSION 49 3.1. Isoflavone reductions by hydride reagents and hydrogenations 49 3.2. Synthesis of trans- and cis-isoflavan-4-ols 51 3.3. Synthesis of isoflav-3-enes 52 3.4. Synthesis of isoflavans 52 3.4.1. Racemic polyphenolic isoflavans 52 3.4.2. Enantiopure polyphenolic isoflavans 53 3.5. Synthesis of -methyldeoxybenzoins 58 3.5.1. Polyphenolic -methyldeoxybenzoins 58 3.5.2. Enantiopure -methyldeoxybenzoins 59 3.6. Isoflavonoids in biological studies 62 3.6.1. S-equol determination from serum of ewes 62 3.6.2. ODMA and equol in human isoflavone metabolism studies 62 3.6.3. Biological activity of S-equol vs. rac-equol in vitro 63 3.6.4 Equol quantitation in organic skimmed Finnish cow milk 63 4. CONCLUSIONS 64 5. EXPERIMENTAL 64 REFERENCES 70 ORIGINAL PUBLICATIONS 77 LIST OF ORIGINAL PUBLICATIONS This thesis is based on the following original publications, which are referred to in the text by their Roman numerals (I-VI): I. Auli K. Salakka, Tuija H. Jokela, Kristiina Wähälä. Multiple hydride reduction pathways in isoflavonoids. Beilstein J. Org. Chem. 2, 2006, No. 16. II. Pihlaja, K., Tähtinen, P., Klika, K.D., Jokela, T., Salakka, A.; Wähälä. K. Experimental and DFT 1H NMR Study of Conformational Equilibria in trans-4’,7-Dihydroxyisoflavan-4-ol and trans-Isoflavan- 4-ol, J. Org. Chem. 68, 2003, 6864. III. Mustonen, Eeva; Jokela, Tuija; Saastamoinen, Ilkka; Taponen, Juhani; Taponen, Suvi, Saloniemi, Hannu; Wähälä, Kristiina. High serum S- equol content in red clover fed ewes: the classical endocrine disruptor is a single enantiomer. Environ. Chem. Lett., 3, 2006, 154-159. IV. Wähälä, K.; Jokela, T. Preparation of isoflavonoids. Finn. 2009, 20 pp. CODEN: