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Synthetic Methods for Biologically Relevant Organofluorine Compounds

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Synthetic Methods for Biologically Relevant Organofluorine Compounds Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Spring 2007 Synthetic methods for biologically relevant organofluorine compounds Meher Perambuduru Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Chemistry Commons Department: Chemistry Recommended Citation Perambuduru, Meher, "Synthetic methods for biologically relevant organofluorine compounds" (2007). Doctoral Dissertations. 2286. https://scholarsmine.mst.edu/doctoral_dissertations/2286 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. t+/ E. : i :_~· f 9;?.::; SYNTHETIC METHODS FOR BIOLOGICALLY RELEVANT ORGANOFLUORINE COMPOUNDS by MEHERPERAMBUDURU A DISSERTATION Presented to the Faculty ofthe Graduate School of the UNIVERSITY OF MISSOURI-ROLLA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY m CHEMISTRY 2007 V. PRAKASH REDDY EKKEHARD SINN ~~ NURANERCAL 111 ABSTRACT This thesis describes novel synthetic methodologies for the synthesis of biologically relevant organofluorine compounds. Chapter 1 outlines the recent trends in this area and our synthetic procedures for the preparation of the gem-difluoromethylene analogues of the biologically active dipeptides, carnosine and carcinine. Synthesis of the latter compounds has been achieved using the fluorinated building block approach. Thus reaction of gem-difluoro-~­ alanine with histidine methyl ester dihydrochloride or histamine dihydrochloride using N­ benzyloxycarbonyl (N-Cbz) protecting strategy and EDCVHOBt peptide coupling protocol gave the gem-difluorinated version of the peptides carnosine and carcinine respectively. The gem­ Difluoro analogue of ~-alanine was prepared from a fluorine synthon, ethyl bromodifluoroacetate using Reforrnatsky reaction conditions. Chapter 2 is focused on development of novel synthetic method for the preparation of gem-difluorodiarylmethanes from the corresponding carbonyl compounds. Thus, 2,2-diaryl-1,3- dithiolanes, readily obtainable from the corresponding diaryl ketones, were converted to the corresponding gem-difluorodiarylmethanes using a novel reagent combination SelectfluorR and Olah's reagent, pyridinium polyhydrogen fluoride (PPHF). This reaction is convenient, effective, and requires simple workup and mild reaction conditions. The reaction, although broadly applicable for diaryl ketones, is not useful for the preparation of their aliphatic versions. Chapter 3 delineates the preparation of trifluoromethylated arylsulfonamides by nucleophilic trifluoromethylation of aromatic N-tosylaldimines using trifluoromethyl trimethylsilane in the presence of N-heterocyclic carbene as a catalyst. N-heterocyclic carbene was produced in situ through the reaction from imidazolium chloride and potassium tert­ butoxide. Aromatic N-tosylaldimines with both electron-withdrawing and electron-donating groups underwent facile trifluoromethylation in the presence ofN-heterocyclic carbene to afford the corresponding trifluoromethylated sulfonamides in moderate to good yields. However, further optimizations are needed for the trifluoromethylation of aliphatic imines using this reagent. IV ACKNOWLEDGMENTS I am deeply grateful to my advisor, Dr. V. Prakash Reddy for his excellent guidance, encouragement and enthusiasm over the years he has provided. I appreciate his patience, insightful comments and for giving me the opportunity to think and learn independently and providing me the freedom in performing the research. Without his mentorship, constant support and caring this thesis would not have been possible. I am thankful to Dr. Ekkehard Sinn, Dr. Yinfa Ma, Dr. Nuran Ercal and Dr. Oliver C. Sitton for serving on my graduate committee and helping me throughout my Ph.D. program. I am particularly thankful to my beloved friend Mr. Ramesh Alleti for his friendship, guidance and support throughout my career and my life. I am greatly thankful to my friends Uday Kumar, Srinivas Reddy Dubbaka, Devender Pinnapareddy, Achanta Srinivas, Vikram kanmukhla, and Srinivas Gorla for putting up with me and for their continuous support, encouragement and contribution. I would like to express my deepest gratitude to my parents, brother and other family members for their abundant love, encouragement, and support in every decision I made and every step I took throughout my life. v TABLE OF CONTENTS ABSTRACT ...................................................................................................................... .iii ACKNOWLEDGMENTS ......................................................................... .iv LIST OF FIGURES ................................................................................viii NOMENCLATURE ................................................................................XV l. SYNTHESIS OF GEM--DIFLUOROMETHYLENE ANALOGUES OF CARNOSINE AND GEM-DIFLUOROMETHYLENE CARCININE ......................... 1 1. l INTRODUCTION ................................................................................................... 1 1.1.1 Fluorinated versions of peptide analogues/mimetics ...................................... 1 1.1.2 Synthetic methods for selected fluorinated peptide analogues ....................... ! 1.1.2.1 Difluorostatone and difluorostatine peptide analogues ....................... 2 1.1.2.2 Difluoroketomethylene peptide isostere ............................................. 6 1.1.2.3 Monofluoro ketomethylene peptide isostere .............................. 9 1.1.2.4 Monofluoro hydroxyethylene peptide isosteres ........................ 10 1.1.2.5 Fluoroalkene and (trifluoromethyl)alkene peptide isosteres .......... 14 1.1.2.6 Fluorinated amino acids and pep tides .................................... 17 1.2 RESULTS AND DISCUSSIONS .......................................................................... 23 1.2.1 Synthesis of gem-difluoromethylene analogue of L-camosine ............... 27 1.2.2 Synthesis of gem-difluoromethylene carcinine ................................. 36 1.3 CONCLUSIONS .................................................................................................... 38 1.4 EXPERIMENTAL RESULTS ............................................................................... 39 1.4.1 General. ............................................................................... 39 1.4.2 Synthesis and properties of products ............................................ .40 1.4.3 NMR spectra of the products ...................................................... 60 VI 1.5 REFERENCES ............................................................................. 82 2. A NOVEL AND CONVENIENT SYNTHETIC METHOD FOR THE PREPARATION OF GEM-DIFLUORODIARYLMETHYLENE COMPOUNDS ... 89 2.1 INTRODUCTION .................................................................................................. 89 2.1.1 Aldehydes and ketones to gem-difluoromethylene compounds ................. 90 2.1.2 Hydrazones and Oximes to gem-difluoromethylene compounds......... 93 2.1.3 Dithioacetals and dithioketals to gem-difluoromethylene compounds ....... 95 2.1.4 Thiocarbonyls to gem-difluoromethylene compounds ............................... 97 2.1.5 Azirines to gem-difluoromethylene compounds ............................... 98 2.1.6 Olefinic and acetylenic compounds to gem-difluoromethylene compounds ......................................................................... 98 2.1.6.1 Alkenyl trifluoroborates .................................................. 98 2.1.6.2 Alkenes ..................................................................... 99 2.1.6.3 Allylamines ............................................................... 100 2.1.6.4 Alkynes ................................................................... 101 2.1. 7 Electrophilic difluorination ...................................................... 102 2.2 RESULTS AND DISCUSSIONS ........................................................................ 104 2.3 CONCLUSIONS .................................................................................................. 11 0 2.4 EXPERIMENTAL RESULTS ............................................................................. 110 241General. ································· ............................................ 110 2.4.2 General procedure for the preparation of gem-difluoromethylene compounds .................... ················································· .110 2.4.3 Synthesis and properties of products .......................................... 111 2.4.5 NMR spectra ofproducts ................... ··· ...... ··· · ·· · ········· ·· ........... 116 2 .5 REFERENCES ······························ ............................................. 119 Vll 3. CARBENE CATALYZED TRIFLUOROMETHYLATIONS OF AROMATIC N- TOSYL-ALDIMINES ...................................................................... 124 3.1 INTRODUCTION ....................................................................... 124 3.1.1 Nucleophilic trifluoromethylation ofimines .................................. l24 3.1.2 N-Hetereocyclic carbene as a catalyst. ......................................... 130 3.2 RESULTS AND DISCUSSIONS ..................................................... 135 3.3 CONCLUSIONS .......................................................................
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