PART I: A CONCISE TOTAL SYNTHESIS OF MICROTUBULE INHIBITORS TRYPROSTATIN A, B AND THEIR ANALOGS PART II: EVALUATION OF AN APPROACH FOR THE C2 ALKYLATION OF GRAMINE

Abstract

PART I: A CONCISE TOTAL SYNTHESIS OF MICROTUBULE INHIBITOR TRYPROSTATIN A AND B AND THEIR ANALOGSTryprostatins A and B are natural products that exhibit anticancer properties. They were originally isolated from Aspergillus fumigatus, in trace amounts. These natural products are microtubule inhibitors and completely inhibit cell cycle progression of tsFT210 cells at the G2/M phase, at final concentrations of 50 μg/mL and 12.5 μg/mL, respectively. The proposed mechanism of action for these compounds involves interference with the interaction between microtubule-associated protein 2 and the C-terminal region of tubulin. Additionally, it has been shown that tryprostatin A inhibits breast cancer resistance protein meaning it has potential to reverse multidrug resistance found in some cancers. This intriguing biological activity coupled with their simple structure has inspired interest in the synthetic community resulting in a few reported total syntheses. Here, we report a concise four-step total synthesis of tryprostatins A and B that has been developed. This synthesis started from commercially available gramine. The key step features a coupling between a C2,N′-diprenylated gramine salt and a diketopiperazine, mediated by quinine as a bifunctional base. The synthesis afforded tryprostatins A and B along with their respective epimers in 1:1 ratios, as determined by isolation and separation via column chromatography. The overall combined yields were 22% for tryprostatin A and its epimer, and 44% for tryprostatin B and its epimer. Additionally, this synthetic method has been extended to 5-methoxy tryprostatin analogs which had an overall combined yield of 11%. The synthesis of several other analogs has been started. Some of the analogs have had preliminary biological assays performed that prove they are active compounds. Lastly, in silico studies have been performed to guide the choice of the next analogs to make. PART II: EVALUATION OF AN APPROACH FOR THE C2 ALKYLATION OF GRAMINE C2-substituted indoles are often considered “privileged structures” because they can engage a wide range of biological targets with high affinity. That fact paired with our group’s interest in synthesizing tryprostatins led us to further investigate our simple alkylation at the C2 position of N-protected gramines under relatively mild reaction conditions. The designed transformation involves the reaction of N-protected gramines with n-BuLi and a variety of alkyl halides to produce C2,N’-dialkylated gramine salts in moderate to high yield. We expanded the scope of the reaction in terms of electrophiles and protecting groups. Then the mechanism was probed which resulted in us demonstrating that both gramine’s methylene N and the indole’s protecting group, such as Boc, cooperate to stabilize C2 lithiation and provide the highest conversion to the product. The generation of novel C2,N’-dialkylated gramine salts while be important for the synthesis of tryprostatin analogs with potential for utility in synthesizing other natural products.