University of Bath PHD Synthesis of isocyanide derived natural products with antibiotic activity Blackburn, Richard Award date: 2016 Awarding institution: University of Bath Link to publication Alternative formats If you require this document in an alternative format, please contact: [email protected] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 04. Oct. 2021 Synthesis of isocyanide derived natural products with antibiotic activity Richard Blackburn A thesis submitted for the degree of doctor of philosophy University of Bath Department of Chemistry August 2015 COPYRIGHT Attention is drawn to the fact that the copyright of this thesis rests with its author. A copy of this thesis has been supplied on the condition that anyone who consults it is understood to recognise that its copyright rests with the author and they must not copy or use it or use material from it except as permitted by law or with the consent of the author. This thesis may not be consulted, photocopied or lent to other libraries without the permission of the author for 3 years from the date of acceptance of the thesis. 06 Aug. 15 Abstract This thesis concerns itself with developing methodology for the synthesis of vinyl-isocyanide natural products and evaluating the biological properties of their common aglycone’s vinyl- isocyanide warhead. Firstly, methodology for the total synthesis of isocyanide containing natural products isolated from terrestrial and marine sources is reviewed, describing the different strategies that have been employed for their synthesis as well as any associated biological activity. The development of a novel isocyanide derived phosphonate ester and its use in an E-selective Horner-Wadsworth-Emmons protocol for the synthesis of the agylcone, phenol vinyl- isocyanide, from p-hydroxybenzaldehyde is then descrided. It was found that increasing the steric bulk of phosphonate ester groups increased the E-selectivity of homologation from 7 : 3 to 9 : 1. Total selectivity was subsequently achieved when temporarely reducing the acidity of the substrates through phenol silylation, although these species typically began to isomerise upon desilylation and isolated samples of phenol vinyl-isocyanide typically possesed >95 d.e. Phenol vinyl-isocyanide is then demonstrated as a potent melogenesis and bacterial inhibitor with low toxicity, leading us to develop some antibiotic structure activity relationships. Having synthesised the agylcone, we intended to use this in the total synthesis of Rhabduscin and Byelyankacin. Being an unstable species, methology was then developed for the synthesis of these rhamnopyranosides using p-hydroxybenzaldehyde for the glycosylation step. The previously developed Horner-Wadsworth-Emmons reagent was then used to achieve the first synthesis of Byelyankacin. Work is on-going towards completing the synthesis of a suitable rhamnopyranoside aldehyde for the synthesis of Rhabdusin using the same synthetic operations reported for Byelyankacin. Finally, we report the synthesis of Paerucumarin, an isocyanide derived di-hydroxy coumarin species that has a related biosynthesis to Byelyankacin, Rhabduscin and their common glycone This synthesis procedes via the structurally related natural product, Pseudoverdin. ii CONTENTS 1 Literature Review – Methodology for the synthesis of isocyanide containing natural products (covering up to end of 2014) 1 1.1 Introduction 1 1.2 Syntheses of marine isocyanides derived from sesquiterpene biosynthetic pathways 9 1.3 Syntheses of isocyanides derived from L-tyrosine or L-tryptophan 49 1.4 Syntheses of miscellaneous isocyanide natural products 80 1.5 Conclusion 86 2 The development of an E-selective Horner-Wadsworth-Emmons protocol for the synthesis of phenol-vinyl isocyanide 88 2.1 Insects as a source of Natural Products 88 2.2 Life cycle of heterorhabdus nematodes. 89 2.3 Inhibition of tyrosinases by Rhabduscin and Byelyankacin 90 2.4 Antibacterial activity of structurally related vinyl isocyanides 93 2.5 Project Outline 95 2.6 Biosynthesis of Rhabduscin and Byelyankacin 95 2.7 Use of Schöllkopf’s reagent for the synthesis of vinyl-isocyanide aglycone 542. 96 2.8 Synthesis of phenyl vinyl-isocyanide 542 100 2.9 Synthesis of p-hydroxy phenyl vinyl-isocyanide 542 102 2.10 Development of novel, bulkier phosphonate. 111 2.11 Protection of phenol functionality. 112 2.12 Final conditions and synthesis of phenol-vinyl isocyanide (aglycone). 115 2.13 Conclusion 116 iii 3 Biological evaluation of phenol vinyl-isocyanide 117 3.1 Melogenesis suppression 117 3.2 Antibiotic Activity 119 3.3 Structure Activity Relationships 122 3.4 Library of phenols 125 3.5 Isostere synthesis 126 3.6 Conclusions 127 4 Methodology for the Synthesis of Byelyankacin and Rhabduscin 129 4.1 Introduction 129 4.2 Synthesis of Byelyankacin 130 4.3 Attempts to fix E selectivity for sugar natural products 136 4.4 Synthesis of Rhabduscin 139 4.5 Conclusions 145 5 Synthesis of Paerucumarin 146 5.1 Introduction 146 5.2 Synthesis of Pseudoverdin and Paerucumarin 147 5.3 Conclusions 152 6 Experimental 153 6.1 General Considerations and Procedures 153 6.2 Compounds associated with the development of E-selective Horner Wadsworth Emmons Reaction (chapter 2). 158 6.3 Biological evaluation of phenol vinyl-isocyanide (Chapter 3). 165 iv 6.4 Compounds associated with the synthesis of Byelyankacin and Rhabduscin (Chapter 4) 177 6.5 Compounds associated with the synthesis of Paerucumarin (Chapter 5) 193 6.6 Biological Procedures/Investigations 196 6.7 Computation calculations using Spartan 197 7 References 198 v Acknowledgements There is only one person with which to start this section, Dr. Steven Bull. I want to thank him so much for taking me on, giving me his advice, support and patience over what has seemed a very quick four years. He has always been so much more than ‘just’ a supervisor and he should know how much I value his friendship. Jointly, I would like to thank him and Professor Tony James for all the opportunities they have afforded me, and the fantastic time I have had here in Bath, and travelling around the world because of them. The memories of our joint trips will haunt me (in a good way) for the rest of my life. Liam Stephens and Diana Alves are to be thanked for their hard work in biology and the many hours spent generating the ‘numbers’ reported in chapter 3. It should also be highlighted that Liam made five of the compounds used in this chapter and for that he has been paid in beer. My fondest memories of the Ph.D. will always be those Friday, and worryingly often mid-week, evenings in the pub with the likes of David Tickell, Robert Chapman, Bill Cunningham, Ben Atkinson and of course the two aforementioned grown-ups. We always had the best intentions, with that one of pint nearly always turning into a ‘few’. Furthermore it has been an absolute pleasure to spend the last four years working alongside so many good friends. I would therefore also like to thank Rob Archer, Paul Fordred, Jen Peed, Lucy Peacock, Ruth Lawrence, Amy Groome, Caroline Jones, Emma Lampard, Adam Sedgwick, Anqi Jiang and Marc Hutchby for contributing massively to my time in Bath. Finally, my long suffering parents Carol and Andrew, sister Jenny and highly tolerant fiancé Charlotte all deserve a mention. They have loved me unconditionally and have supported me in all that I have done and strive to do. vi Abbreviations AFA acetic formic anhydride approx. approximately b.p. boiling point Bn benzyl br. broad Bu Butyl CDMT 2-Chloro-4,6-bis[3-(perfluorohexyl)propyloxy]-1,3,5-triazine CPBA chloroperbenzoic acid CSA camphor sulfonic acid d doublet DBU 1,8-Diazabicyclo[5.4.0]undec-7-ene dd doublet of doublets ddd doublet of doublets of doublets delta chemical shift DIBAL diisobutylaluminum hydride DIEA N,N-Diisopropylethylamine DIPEA diisopropyl amine DMAP dimethyl aminopyridine DMAP dimethylaminopyridine DMF N,N-dimethylformamide DMP Dess-Martin periodinane DMSO dimethyl sulfoxide DMT dimethoxytriphenylmethyl e.g. for example EC50 half maximal effective concentration equiv. equivalent Et ethyl Fig. figure g gram h. hour HMPA hexamethylphosphoramide HWE Horner-Wadsworth-Emmons Hz Hertz i iso IBX 2-Iodoxybenzoic acid IC50 half maximal inhibitory concentration inc including IR infra red IUPAC international union of pure and applied chemistry J coupling constant KHMDS potassium hexamethyldisilazane LDA lithium diisoproplyamine LHMDS lithium hexamethyldisilazane Ltd. limited vii m meta M Mega m multiplet m.p. melting point Me methyl mg milligram MIC minium inhibitory concentration min. minute mL millilitre mM millimolar MOM methoxymethyl MRSA methicillin resistant staphylococcus aureus MS Mass Spec Ms Mesyl NBS N-bromosuccinamide NCS isothiocyanate ng nano gram NHMDS sodium hexamethyldisilazane NIS