This thesis describes the synthesis of novel analogs of the unique opioid receptor modulator mitragynine along with pharmacological and behavioral studies of a subset of its novel analogs. In Chapter 1, a general overview of opioid receptors and the importance of the mu opioid receptor (MOR) for the treatment of pain is provided. The rise of the opioid epidemic is discussed which brings into attention the need to develop safer opioid therapeutics for the treatment of pain. In this regard the Mitragyna indole alkaloids, isolated from kratom leaves are of great interest as they are considered to be “atypical” opioid ligands and represent novel molecular scaffolds for the development of safer opioid receptor modulators. The introductory chapter includes a brief description of the pharmacological profile of mitragynine as a prelude to the work that follows – examining unexplored positions on the alkaloid by devising new methodology and synthetic routes to synthesize novel analogs to study its structure-activity relationship (SAR) at the opioid receptors. Chapter 2 describes the development of a new synthetic method for selective functionalization of the unexplored C11 position of the MG scaffold (C6 position in indole numbering). The method takes advantage of an indole-ethylene glycol adduct as a key intermediate which can undergo subsequent iridium-catalyzed borylation at the desired position. This late-stage C(sp2)-H functionalization approach provides a practical route to novel C11-analogs of mitragynine and related scaffolds starting from the natural product, thus allowing a systematic SAR exploration of the C11 position. Chapter 3 directly builds on Chapter 2, summarizing the neuropharmacological and behavioral studies on the C11 analogs of 7-hydroxymitragynine (7OH) and mitragynine ethylene glycol (MG-EG). Through these studies we discover that the C11 position represents a key locant for fine-tuning opioid receptor signaling efficacy. We also discuss that the parent 7-hydroxymitragynine (7OH), a low efficacy agonist, is transformed to an even lower efficacy agonist by introducing a fluorine substituent at the C11 position (11-F-7OH). This is demonstrated in vitro at both mouse and human mu opioid receptors (mMOR/hMOR) and in vivo in mouse analgesia tests. Low efficacy opioid agonists are of high interest as candidates for generating safer opioid therapeutics with mitigated side effects. Thus, this section concludes with the identification 11-F-7OH as lead compound for future investigation. Chapter 4 describes our attempts towards the functionalization of another unexplored and vital position for the activity of mitragynine at the mu opioid receptor (MOR) – the ethyl group at the C20 position. This chapter illustrates our extensive efforts towards the late-stage functionalization of the ethyl group in the C20 position of mitragynine via directed C(sp3)-H activation. Various strategies including using the mitragynine ethylene glycol (MG-EG) as a bidentate ligand or manipulating the acrylate ester group on mitragynine as a directing group are discussed in the chapter. Also described are all the screened reaction conditions using palladium catalysts and various ligands starting from pyridine-based to mono-protected amino acid-based ligands. The outcomes and hypotheses for the failures of each strategy employed are also presented in the chapter. Chapter 5 describes our efforts towards the de novo synthesis of the C20 analogs, as an alternative strategy to the failed late-stage functionalization from Chapter 4. We present a strategy to synthesize the C20 analogs through a diversification strategy from a common intermediate. We further discuss the results of our efforts towards the formal synthesis of this common intermediate. The chapter concludes with a discussion of an alternate strategy for the synthesis of the C20 analogs.

La spéciophylline (ou Uncarine D) est une molécule extraite d’une plante africaine endémique Mitragyna inermis qui présente une activité antipaludique contre la souche chloroquinorésistante W2 de Plasmodium falciparum, un des parasites responsables du paludisme. Son mode d’action est encore inconnu et des quantités plus importantes de produit naturel sont nécessaires pour poursuivre les études d’activité biologiques. Ces quantités ne peuvent être fournies par extraction des feuilles de Mitragyna inermis. Les objectifs de ce travail ont été d’établir une méthodologie de synthèse énantiosélective du motif spiranique de la spéciophylline pour en réaliser la synthèse totale, d’étudier l’activité antiplasmodiale de sous-structures afin de déterminer le pharmacophore de la spéciophylline et de fournir des quantités suffisantes de spéciophylline pour continuer l’étude du mode d’action de cette molécule. / Speciophyllin (or Uncarine D) is a natural product extracted from the endemic African plant Mitragyna inermis. It is active against Plasmodium falciparum’s chloroquine-resistant strain W2 which is one of the malaria responsible parasites. Speciophyllin’s action pathway remains unknown and more important amounts that cannot be provided by plant extraction are required to go on with the biologic activity studies. The aims of this work were to develop an enantioselective synthetic methodology to access speciophyllin’s spiranic core to be able to achieve its total synthesis. Through substructures synthesis and antiplasmodial activity evaluation we could study speciophyllin’s pharmacophore.

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