Isocyanate chemistry is well-known and has been studied and exploited for years. N-Isocyanate derivatives, however, are scarce and far less understood. These are divided in three subclasses: the aminoisocyanates, the iminoisocyanates, and the rarest of them all, the amido-isocyanates. The latter are underdeveloped and understudied. Herein, studies that resulted in evidence for the existence of N_β-amido–isocyanates, and validated their use in a masked isocyanate strategy, will be described. Suitable precursors, N_β-acyl phenylcarbazide derivatives (activated aza-dipeptides), were synthesized in the context of aza-tripeptide synthesis. The 1,3,4-oxadiazol-2(3H)-one intermediate was formed quickly in the course of the reaction, and an equilibrium between the free N_β-amido-isocyanate and the 1,3,4-oxadiazol-2(3H)-ones was established. Longer reaction times, in presence of amino amide nucleophiles, led to the formation of hydantoins or aza-tripeptides with full consumption of both the starting material and the oxadiazolone intermediate, yielded 14 hydantoins and 4 aza-tripeptides in 51-79% isolated yields. Experiments were performed to support the formation of an amido-isocyanate intermediate and discriminate between pathways possibly involving the formation of a tetrahedral oxyanionic intermediate versus the trapping of an N-isocyanate by a nucleophile. A control reaction in which the N_α in the starting material was methylated completely suppressed the formation of the isocyanate intermediate and shut down the reaction, lending supporting the isocyanate formation pathway. The hydrogen at this position is crucial for the formation of the isocyanate, which can be deprotonated and form a neutral isocyanate species. To further support the mechanistic hypothesis, established C-isocyanate chemistry, in which isocyanates react with carboxylates to form amides, was applied to a series of oxadiazolones. This transformation cannot occur in the absence of an isocyanate. This reaction yielded 8 different N_β-acyl hydrazides with moderate to good yields, again supporting the formation of the rare amido-isocyanates. Overall, this work supports the formation of amido-isocyanates in equilibrium with their corresponding 1,3,4-oxadiazol-2(3H)-ones and validated that the latter are masked amido-isocyanates, species that have been rarely studied in the literature.

Both clan CA and clan CD proteases have a variety of physiological and pathological roles. In particular, both clans have members who have been implicated in cell death pathways, including apoptosis. Caspases are members of clan CD. Many of the caspase inhibitors used in apoptotic studies have shown cross reactivity with clan CA proteases. Thus, the anti-apoptotic effect of these inhibitors could be due to the broad-spectrum inhibition of a variety of cysteine proteases. Recently, the Powers laboratory designed a new class of inhibitors highly specific for clan CD proteases, aza-peptide epoxides. Initial data showed that this high selectivity could be due to the presence of the aza-residue, and not simply an artifact of substrate specificities. E-64c, an epoxysuccinyl inhibitor, is known to be a highly potent inhibitor of cathepsin B and calpain I. Thus, to determine if these clan CA proteases could tolerate an aza-residue, aza-E-64c and its analogues were synthesized. These inhibitors, termed epoxysuccinyl aza-peptides, were found to be significantly less potent for cathepsin B, calpain I, and papain than their non-aza counterparts, including E-64c. Previous findings have shown that the reactivity and selectivity of aza-peptide epoxides with caspases were significantly influenced by epoxide stereochemistry and the prime side substituent. Thus, this second project involved the systematic study of epoxide stereochemistry effects, prime side substituent effects, and the combined effect of these two variables. All inhibitors were tested with the seven apoptotic caspases: caspases-2, -3, -6, -7, -8, -9, and -10. We found that epoxide stereochemistry, prime side substituent, and also the peptidyl sequence have combined effects on potency and selectivity. In general, the (S,S) stereoisomer is the most potent relative to the (R,R) and (cis) stereochemistries. Modeling studies were done to determine why this is true. Aza-peptide epoxides were also briefly compared to aza-peptide Michael acceptors, another class of inhibitors highly specific for clan CD proteases

Les prodrogues sont des dérivés biologiquement inactifs d’un principe actif qui, après administration à un organisme, subissent une transformation chimique ou enzymatique pour libérer le principe actif au site d’action. Elles améliorent les propriétés physicochimiques du principe actif pour permettre un meilleur transport à travers les barrières biologiques et pour augmenter l’activité in vivo. Elles sont utilisées pour améliorer la formulation et l’administration, accroître la perméabilité et l’absorption, modifier le profil de distribution et éviter le métabolisme et la toxicité. Cette approche est très utile pour améliorer l'administration de principes actifs. Il existe deux types de prodrogues : les prodrogues liées à un transporteur et les bioprécurseurs. Dans le premier cas, la molécule active est liée par une liaison covalente à un groupement temporaire, ce qui fournit une nouvelle molécule, qui est inactive. Le groupement temporaire libéré ne doit pas avoir, par lui-même, d'action pharmacologique ni de toxicité. Dans le second cas, le principe actif est transformé métaboliquement ou chimiquement par réaction d’hydratation, d’oxydation ou de réduction. Les azapeptides sont des mimes peptidiques dans lesquels un ou plusieurs carbones de la chaîne peptidique sont remplacés par des atomes d’azote. Ce remplacement augmente la rigidité de la chaîne peptidique et favorise le repliement de type β. Le repliement β des azapeptides est associé à plusieurs propriétés thérapeutiques. Certains azapeptides ont montré une meilleure activité, une meilleure sélectivité et une plus grande stabilité comparativement aux peptides parents ce qui prolonge leur durée d'action et les rend plus résistants aux dégradations métaboliques. Ce mémoire s’intéresse particulièrement à l’azapeptide : [aza(p-MeO)F⁴]-GHRP-6. Celui-ci est un analogue du peptide sécréteur d’hormone de croissance 6 (GHRP-6, H-His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂), qui possède une affinité pour deux récepteurs distincts : les récepteurs de growth hormone secretagogue receptor 1a (GHS-R1a) et le récepteur cluster of differentiation 36 (CD36). L’[aza(p-MeO)F⁴]-GHRP-6 démontre une sélectivité envers le récepteur CD36 offrant des possibilités de traitement de maladies telles que l’athérosclérose et la dégénérescence maculaire liée à l’âge (DMLA). De plus, le récepteur CD36 peut interagir avec un corécepteur toll-like receptor 2 (TLR2), et l’[aza(p-MeO)F⁴]-GHRP-6 peut réduire des réponses immunitaires innées. La stratégie des prodrogues a été utilisée dans ce mémoire pour augmenter la durée d’action de l’azapeptide [aza(p-MeO)F⁴]-GHRP-6. Plus précisément, cinq analogues des prodrogues α-acyloxyéthylcarbamates de l’aza(p-MeO)F⁴-GHRP-6 ont été synthétisées. Ce mémoire présente la première synthèse de prodrogues α-acyloxyéthylcarbamates à caractère PEG de l’[aza(p-MeO)F⁴]-GHRP-6. / A prodrug is a biologically inactive derivative of a drug which after administration undergoes chemical or enzymatic modification to release the active drug at targeted sites of activity. Prodrugs improve physicochemical properties to enable better transport through biological barriers and enhance activity. They are used to improve formulation and administration, to enhance permeability and absorption, to modify distribution profiles and to avoid metabolism and toxicity. The prodrug approach is useful for improving drug delivery. Prodrugs are classified into two types: carrier-linked prodrugs and bio-precursors. In the first case, the parent drug is linked by a covalent bond to an inert carrier or transport moiety. The carrier should not be active or toxic. The active drug is released by a chemical or enzymatic cleavage in vivo. In the second case, the parent drug is converted metabolically or chemically by hydration, oxidation or reduction reactions. Azapeptides employ a semicarbazide as an amino amide surrogate in a peptide analog in which the backbone α-CH is replaced by nitrogen. Through electronic interactions, the semicarbazide favors backbone β-turn geometry due to a combination of urea planarity and hydrazine nitrogen lone pair – lone pair repulsion. Azapeptides have proven therapeutic utility. Some of them exhibit better selectivity, activity and stability than the parent peptides with increased duration of action and improved metabolic stability. Growth hormone releasing peptide-6 (GHRP-6, H-His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂) is a synthetic peptide possessing an affinity for two different receptors: growth hormone secretagogue receptor 1a (GHS-R1a) and cluster of differentiation receptor 36 (CD36). The GHRP-6 azapeptide analogue, [aza(p-MeO)F⁴]-GHRP-6, has exhibited good affinity for CD36 and reduced nitric oxide overproduction in macrophage cells stimulated with the TLR-2 agonist R-FSL-1. Azapeptide ligands of CD36, such as [aza(p-MeO)F⁴]-GHRP-6, offers potential as prototypes for developing treatments of diseases such as atherosclerosis and age-related macular degeneration. A prodrug strategy has been pursued to improve the pharmacokinetic properties, such as duration of action, of [aza(p-MeO)F⁴]-GHRP-6. The first examples of α-acyloxyethyl carbamate peptides have been prepared. Five α-acyloxyethyl carbamate analogues of [aza(p-MeO)F⁴]-GHRP-6 have been synthesized by routes featuring acylation of the resin-bound peptide using different activated α-acyloxyethyl carbonates prior to resin cleavage and side chain deprotection. The evaluation of the activity of the pharmacokinetic properties of the [aza(p-MeO)F⁴]-GHRP-6 prodrugs is currently in progress and will be reported in due time.