22 AUGUST 2022 | VOL 8 | 1 Journal of Emerging Investigators • www.emerginginvestigators.org INTRODUCTION For decades, neuroactive alkaloids isolated from naturally occurring phytochemical sources have been crucial in the identification and optimization of small molecules with potency in treating neurological disorders (1,2). Some natural products have gone on to inspire the development of synthetic analogs, which might possess greater potency or better pharmacological features than the natural product itself. One such naturally occurring alkaloid, physostigmine, which is found in the calabar bean plant Physostigma venenosum, has been demonstrated to be a potent cholinesterase inhibitor (3). Specifically, physostigmine possesses an N-methylcarbamate moiety, which reversibly acylates the active site serine in acetylcholinesterases, rendering such enzymes inactive in breakdown capabilities of acetylcholine, a neurotransmitter (4). This results in acetylcholine accumulations near cholinergic synapses in the central nervous system, allowing for continued chemical messaging in the parasympathetic nervous system (5). Despite its potency as an enzyme inhibitor, physostigmine’s low bioavailability, short half life of 16 minutes due to autohydrolysis of the N-methylcarbamate, and acute toxicity has limited its therapeutic potential (6 - 9). These challenges have prompted the development of rivastigmine, a synthetic amino carbamate small molecule that is inspired by and structurally analogous to physostigmine (Figure 1). In 2000, rivastigmine was approved by the United States Food and Drug Administration (FDA) to treat neurodegenerative diseases such as dementia, Alzheimer’s disease, and Parkinson’s disease (10 - 12). Acetylcholinesterase (AChE), the enzyme that breaks down acetylcholine (ACh), has two binding sites for ACh: an anionic site and an esteratic site. Modular mimics of neuroactive alkaloids - design, synthesis, and cholinesterase inhibitory activity of rivastigmine analogs SUMMARY The treatment of neurological diseases has evolved to include neuroactive alkaloids isolated from naturally occurring phytochemical sources. While some of these compounds have gone on to clinical use themselves, others have inspired the development of synthetic analogs, which might possess greater potency or better pharmacological features than the natural product itself. One such naturally occurring alkaloid, physostigmine, which is found in the Calabar bean plant Physostigma venenosum, has been demonstrated to be a potent cholinesterase inhibitor. However, some of physostigmine's characteristics limit its therapeutic potential, prompting the development of rivastigmine, a similarly structured synthetic compound. The research in our group focused on the synthetic optimization of rivastigmine and its analogs, utilizing computer modeling and biological assays to determine the most favorable analog for inhibition of acetylcholinesterase (AChE), the enzyme that breaks down the neurotransmitter acetylcholine (ACh) to terminate neuronal transmission and signaling between synapses. Patients with Alzheimer’s Disease have lower levels of ACh, which has been associated with symptoms like memory impairment and confusion. The inhibition of AChE allows for ACh accumulation and continued signaling in parasympathetic nervous system. Through our studies, we determined that rivastigmine and its analogs were less effective at inhibiting AChE than physostigmine, and their biological activity is governed by sterics. Erika Yu 1,2 , Shloka Raghavan 1,2 , Shreya Anand 1,3 , Harrison Xu 1,4 , Tvisha Nepani 1,5 , Niharika Nambiar 1,4 , Julia Vu 1,6, Alivia Zhang 1,7 , Suhani Babu 1,4 , Elena Brierley-Green 1,8 , Anushka Peer 1,9 , Alice Finkelstein 1,10 , Adrienne Ferguson 1,11 , Udbhav Avadhani 1,12 , Sanhita Nittala 1,13 , Edward Njoo 1 1 Department of Chemistry, Biochemistry, & Physics, Aspiring Scholars Directed Research Program, Fremont, CA 2 Amador Valley High School, Pleasanton, CA 3 Los Altos High School, Los Altos, CA 4 Dougherty Valley High School, San Ramon, CA 5 Milpitas High School, Milpitas, CA 6 The Quarry Lane School, Dublin, CA 7 American High School, Fremont, CA 8 Palo Alto High School, Palo Alto, CA 9 James Logan High School, Union City, CA 10 Carlmont High School, Redwood City, CA 11 Prospect High School, San Jose, CA 12 Leigh High School, San Jose, CA 13 California High School, San Ramon, CA Article