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Synthesis of 1,2,4 Oxadiazol-5-Imine, 1,2,4-Triazol-3-Imine and Derivatives: a Substituted Cyanamide-Based Strategy for Heterocycle Synthesis

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Synthesis of 1,2,4 Oxadiazol-5-Imine, 1,2,4-Triazol-3-Imine and Derivatives: a Substituted Cyanamide-Based Strategy for Heterocycle Synthesis Synthesis of 1,2,4 oxadiazol-5-imine, 1,2,4-triazol-3-imine and derivatives: A Substituted Cyanamide-based Strategy for Heterocycle Synthesis Shreesha V. Bhat A thesis submitted in partial fulfilment of the requirements of the University of Lincoln for the degree of Doctor of Philosophy June 2017 Statement of Originality “I, Shreesha V. Bhat, hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been published or accepted for the award of any other degree or diploma at University of Lincoln or any other educational institution, except where references have been made in the thesis. Any contribution made to the research by others, with whom I have worked at the University of Lincoln or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.” (Shreesha V. Bhat) ii | P a g e Abstract Considering the importance of nitrogen-rich heterocycles in drug discovery, a novel strategy towards heterocycle synthesis was envisioned using cyanamide chemistry. Synthesis which involve mild conditions, avoids multi-step sequence and non-toxic reagents are desirable for generation of large combinatorial libraries of drug molecules. We envisaged that the NCN linkage of the cyanamide as well as the concomitant use of the nucleo-and electrophilic centres of the cyanamide could provide a novel synthetic route towards nitrogen heterocycles. The first part (Ch-2) constitute the bulk of the thesis and it focuses on the generation of cyanamide ion and its cyclisative capture with a 1,3-dipole – nitrile oxide in situ. The cycloadduct -1,2,4-oxadiazol-5(4H)-imine was obtained in good yields, which was further transformed into pharmacologically important cores like oxadiazolone and amidines. A library of the different heterocyclic cores was generated, which tolerated a wide variety of functional groups in good to excellent yields. In the second part (Ch-3), we developed a novel protocol for the synthesis of 1,2,4-triazol-3- imine via a formal 1,3-dipolar cycloaddition of in situ generated nitrile imines and cyanamide ion. Further hydrolysis furnished with 1,2,4-triazol-3-one, which is an important core from medicinal chemistry point of view. The concomitant generation and reaction of two reactive species- 1,3-dipoles and cyanamide ion was achieved in a single pot in situ to provide a route towards novel and pharmaceutically important heterocyclic cores. The present work provides a platform for the development of cyanamide derivatives as a ‘single-reagent—diverse-scaffolds’ strategy for time efficient library delivery of structurally diverse molecules. iii | P a g e Acknowledgment I am sincerely and heartily grateful to my supervisor, Dr Pallavi Sharma, for her unwavering support and encouragement. Her knowledge, work ethics and wisdom have always inspired and motivated me. I would like to thank her for standing by me through my mistakes and always giving me the chance to improve further. I have been fortunate to receive all the technical training first-hand from her, and I have learnt a lot in terms of carrying out research projects without the inherent biasness and in a time-bound fashion. All the credit for the completion of the PhD in three years goes to her, as she was always there to give inputs and drive the project to completion. Despite my shortcomings, she has always been patient with me and guided me towards the right direction. I would also like to acknowledge the School of life-Sciences and School of Chemistry, University of Lincoln for a fully funded PhD studentship and the utilisation of research instruments and other facilities. I would also like to thank my lab mates – Dr. Ranga whose company I have always enjoyed. He has been an excellent team-mate to work with and we had some good time in the lab discussing chemistry. I will have to give credit to Abhishek and Anish for maintaining a cheerful lab environment. I will never forget the funny moments we had in the lab. I had developed a great rapport with Anish as we worked late into nights and I have always been amazed by his energy and enthusiasm towards work. I would also like to thank Abhishek for taking the effort to print the final thesis for me. I will always cherish the scientific discussions in the lab with Louis (Dr. Louis Adriaenssens) who has been a great support towards the later part of my PhD. I cannot express my gratitude enough for Martin (Dr. Martin Lear) for his role as the internal evaluator for my MPhil/PhD transfer as well as the PhD viva. I thank him for being so understanding and being patient during the correction process. Special thanks to Dr. John Moses (University of Nottingham) whose support helped us in running the NMR and mass analysis in the first year of PhD when we didn’t have NMR in UoL. I would also like to thank our collaborators - Dr. Robinson (computational studies) and Dr. Stefan (Hsp90 assays). I express my gratitude towards all the technical staff members including Julian, Mathieu, Leonie, Stephen and Elisa for the instrument support, and making sure the instrument is up and running. Special mention must go to Angie who always made sure that we were doing alright in terms of lab resources in JBL. Sincere thanks to all the iv | P a g e technicians including Beverly, Angela, Keith, Dan, Martin, Joel who made our life a lot easier in the lab. I would also like to thank the lecturers I worked with as a GTA including Pallavi, Ruth, Belinda and Jose. Their inputs have helped me in doing my job better. A big thanks to the school administrators Sharon, Emma and Lynn for their efforts in processing all the necessary forms and other important admin work. A sincere thanks to the security staff at JBL including Gavin, Tony, Les, Peter and the late George who always made sure I was alright while working in the evenings and nights in the second-floor labs. Some of the nicest people I have come across in Lincoln was in the JBL second floor research office, with people from different nationalities and culture. I had the pleasure of interacting with Paolo, Nabilah, Praew, Aqssa, Rashidi, Sam, Emily, Maxime and Ben who all made the PG life more interesting in Lincoln. Sharing the PhD journey with Mandy, Tammy and Maria was great as we all started our journey at the same time and could share and relate to each other’s problems common in everyday PhD life. I wish them all the best in their future endeavours. Life would not have been so fun without the friends I have made in Lincoln. It was a pleasure being housemates with Payel and Mriganka, who were like family away from home. Most of my trips across UK have been with them, and those memories will always stay with me in my subconsciousness. I met my brother from another mother, Dr. Mohammed, one of the kindest soul I have come across till date. It always felt like I have known him since long, as we made innumerable trips across Brittania (as his daughter would say) all captured on my camera lens. Our conversations about various topics ranging from culture, religion, middle-east politics, food and life were an absolute delight for my curious mind. Hopefully, we will cross paths again in future. It was a fateful day that I decided to go for a quiz hosted by the graduate school where I teamed up with Anthony, and since then we have been partners in many activities. Right from stealing productive breaks for a game of chess or a snack in the lawn overlooking the architecture building, attending jazz sessions every week or playing pool over weekends, having lunch in the atrium or going on adventurous walking trails, we have been involved in many adrenaline- raising activities which made me cheerful when facing failures in the lab. His enthusiasm towards life and social entrepreneurship has been infectious and awe-inspiring altogether. v | P a g e Another person who was a constant support for me in Lincoln was Subash, the university chaplain. Apart from the role of chaplaincy in organising various multi-faith events which I was a part of, he has been a dear friend and his home was always open for me. Two people who were important in my journey despite the distances spanning continents were Harshit and Dr. Mohit Tyagi. Harshit has been with me since the past 10 years and our friendship has stood the obstacles of time and distance. Dr. Mohit has been a constant inspiration and has always pushed me in the right direction. His guidance while applying for PhD positions and later during the PhD has been of immense value. The most challenging time of my PhD studies were the three months of thesis writing. As I went into a shell isolated from the outside world, seeking solace within myself, my decision to go to the student well-being centre helped me in breaking the pattern I had fallen into quite deeply. The accumulated guilt of not having written enough in the first 1.5 months due to procrastination had lead me into a state I would never wish to return to.
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