Amines are ubiquitous in nature and serve a variety of functions in living organisms. Because of this fact amines are of great biological and pharmaceutical interest. The iridium catalyst (pentamethylcyclopentadienyl) iridium dichloride dimer ([Cp*IrCl2]2) has been used in a number of ways to synthesize new carbon-nitrogen bonds. These studies were directed toward the development of a method for the iridium catalyzed N-alkylation of alpha-amino acid esters as well as the development of a strategy for synthesis of the natural product 275A. We have optimized a method for the N-alkylation for alpha-amino acid esters. Using this method, we have N-alkylated a series of alpha-amino acid esters with a variety of alcohols. We have shown that the N-alkylation of the alpha-amino acid esters works consistently and gives the desired products in moderate to high yields. We have examined the effect of this method on the chiral center of the obtained products by analyzing their optical rotation. Evaluation of these specific rotations indicated racemization was occurring but it is believed that any loss of the chiral center is due to the reaction conditions. Amphibian alkaloids are of great interest to the pharmaceutical and academic communities due to their biological activities. Unfortunately, they are not naturally available in large quantities which makes total synthesis the most common method of generating these compounds for evaluation. One amphibian alkaloid class of interest to us are the Lehmizidines. These are bicyclic ring structures consisting of a 7-member and 5-member ring with a nitrogen bridgehead. The alkaloid, 275A, was selected as a target for a general synthetic approach. This synthetic approach required the synthesis of novel diols. The construction of these diols along with a method for the synthesis of the azepane ring is presented here.

The pyrrolidine and piperidine ring systems are present in a variety of different classes of amphibian alkaloids. We have found the iridium catalyzed N-heterocylization reaction of diols with amines to be very useful for the construction of novel pyrrolidine, piperidine and piperazine derivatives. The scope and utility of the iridium catalyzed N-heterocyclization reaction for the construction of novel anuran scaffolds using amino diols and triols are presented. Studies directed towards the total synthesis of 4,6-disubstituted quinolizidine and (±)-epiquinamide are discussed. The second study is focused on the selective conversion of terminal dienes to primary diols. This conversion has always had problems with regioselectivity and low yields due to polymer formation with carbon chains having more than 7 carbon atoms. An improvement in the yield and regioselectivity was observed with disiamylborane prepared in situ using 2-methyl-2-butene and BH3•DMS. The scope of this method with 7, 8 and 9 carbon chains and different alcohol protecting groups for synthesis of triols is presented.

The focus of these studies has been toward the development of new synthetic methods and procedures for the synthesis of novel compounds with unique biological properties. This research has led to the development of two new synthetic strategies for the construction of two novel amphibian alkaloids. In addition, the efforts have led to the large-scale process for the preparation of a novel analgesic compound. The regioselective ring opening of lactones (δ-valerolactone and γ-butyrolactone) with aryllithium reagents is reported for the construction of a series of δ-hydroxyarylketones and γ-hydroxyarylketones. Both the R and S enantiomers of the amphibian alkaloid noranabasamine were prepared in >30% overall yield with 80% ee and 86% ee, respectively. An enantioselective iridium-catalyzed N-heterocyclization reaction with either (R)- or (S)-1-phenylethylamine and 1-(5-methoxypyridin-3-yl)-1, 5-pentanediol was employed to generate the 2-(pyridin-3-yl)-piperidine ring system in 69-72% yield. A cis-2, 5-disubstitued pyrrolidine building block derived from (-)-Cocaine•HCl was prepared. We utilized this compound as a chiral building block for the formal synthesis of (+)-gephyrotoxin. Using this pyrrolidine building block, Kishi's intermediate was obtained enantiospecifically in 15 steps and 9.4% overall yield. A large-scale process for the preparation of the analgesic compounds SCP-123 and its sodium salt, SCP-123ss•monohydrate has been developed. The process for the preparation of SCP-123 required three synthetic steps with no chromatography, while the process for the preparation of SCP-123ss required four synthetic steps and no chromatography. The overall yields for both SCP-123 and SCP-123ss were 47% and 46%, respectively, and both compounds were obtained in exceptionally high purity (>99%).