Sunkyu Han

The concise and enantioselective total syntheses of (-)-trigonoliimines A, B, and C are described. Our unified strategy to all three natural products is based on asymmetric oxidation and reorganization of a single bistryptamine, a sequence of transformations with possible biogenetic relevance. We revise the absolute stereochemistry of (-)-trigonoliimines A, B, and C.

We report three distinct, peptide-based catalysts that enable site-selective phosphorylation of three distinct hydroxyl groups within the complex glycopeptide antibiotic teicoplanin A2-2. Two of the catalysts are based on a design that capitalizes on a catalyst-substrate interaction that mimics the biological mechanism of action for teicoplanin. These catalysts are based on a DXaa-DXaa peptide motif that is known to target the teicoplanin structure in a specific manner. The third was identified

A full account of our concise and enantioselective total syntheses of all known (-)-trigonoliimine alkaloids is described. Our retrobiosynthetic analysis of these natural products enabled identification of a single bistryptamine precursor as a precursor to all known trigonoliimines through a sequence of transformations involving asymmetric oxidation and reorganization. Our enantioselective syntheses of these alkaloids enabled the revision of the absolute stereochemistry of (-)-trigonoliimines A,

The first total synthesis of dimeric securinega alkaloid (-)-flueggenine C is completed via an accelerated intermolecular Rauhut-Currier (RC) reaction. Despite the numerous reports on the total synthesis of monomeric securinegas, the synthesis of dimeric securinegas whose monomeric units are connected by a putative enzymatic RC reaction has not been reported to date. We have found that installation of a nucleophilic functional group at the γ-position of an enone greatly accelerates the rate of t

Abstract Natural product synthesis has lain at the heart of organic chemistry. Complex structures of natural products have inspired chemists to develop new methods and strategies. The utility and robustness of newly developed methodologies have been tested by their application into total synthesis. With the necessity to establish a solid health‐related and biomedical Korean industrial ecosystem, a historically belittled sector when compared to well‐invested manufacturing and electronics industri

Biosynthetic processes often involve reorganization of one family of natural products to another. Chemical emulation of nature's rearrangement-based structural diversification strategy would enable the conversion of readily available natural products to other value-added secondary metabolites. However, the development of a chemical method that can be universally applied to structurally diverse natural products is nontrivial. Key to the successful reorganization of complex molecules is a versatil

We completed the synthesis of dimeric high-oxidation-state securinega alkaloid flueggeacosine B via two synthetic routes from allosecurinine. The first-generation synthesis (seven overall steps) involved a Liebeskind-Srogl cross-coupling reaction for the union of two functionalized fragments, the organostannane and the thioester. As a means to further streamline the synthetic route, we have developed a visible-light-mediated Cu-catalyzed cross-dehydrogenative coupling (CDC) reaction between an a

Abstract Presented here is a concise synthesis of secu′amamine A, and fluvirosaones A and B from readily available allosecurinine and viroallosecurinine. The key C2‐enamine derivative of (viro)allosecurinine, the presumed biosynthetic precursors of these natural products, was accessed, for the first time, by a VO(acac) 2 ‐mediated regioselective Polonovski reaction. Formal hydration and 1,2‐amine shift of this pluripotent enamine compound afforded secu′amamine A. Formal oxidative [3+2] cycloaddi

STING, a central protein in the innate immune response to cytosolic DNA, has emerged as a hot target for the development of vaccine-adjuvants and anticancer drugs. The discovery of potent human-STING (hSTING) agonist is expected to revolutionize the current cancer immunotherapy. Inspired by the X-ray crystal structure of DMXAA (5,6-dimethylxanthenone-4-acetic acid) and hSTINGG230I complex, we designed various DMXAA derivatives that contain a hydrogen bonding donor/acceptor or a halide at the C7

Securinega alkaloids have fascinated the synthetic chemical community for over six decades. Historically, major research foci in securinega alkaloid synthesis have been on the efficient construction of the fused tetracyclic framework that bears a butenolide moiety and tertiary amine-based heterocycles. These "basic" securinega alkaloids have evolved to undergo biosynthetic oxidative diversifications, especially on the piperidine core. However, a general synthetic solution to access these high-ox

Conspectus Securinega alkaloids, composed of more than 100 members characterized by the compact tetracyclic scaffold, have fascinated the synthetic community with their structural diversity and notable bioactivities. On the basis of the structural phenotype, oligomerizations and oxidations are major biosynthetic diversification modes of the basic Securinega framework. Despite the rich history of synthesis of basic monomeric Securinega alkaloids, the synthesis of oligomeric Securinega alkaloids,

We present an ac-coupled scheme for burst-mode optical receivers optimized for 8B/10B line code. The cutoff frequencies of the ac-coupled circuits are carefully adjusted to achieve fast response with minimal distortion to the 8B/10B signal spectrum. The proposed scheme is simple and technically feasible due to its adaptability to well-established continuous-mode components. The burst-mode penalty of the ac-coupled receiver is also investigated using numerical analysis. The numerical results are

The isolation of flueggenines A and B by Yue and co-workers in 2006 has triggered a burst of isolation reports of dimeric and oligomeric securinega alkaloid natural products. The compelling molecular structures of these compounds with various modes of connection between monomeric securinega units have posed intriguing challenges to the synthetic organic community. Herein, we have categorized high-order securinega alkaloids based on their biosynthetic mode of dimerization or oligomerization. We t

We report the X-ray crystal structure of a site-selective peptide catalyst moiety and teicoplanin A2-2 complex. The expressed protein ligation technique was used to couple T4 lysozyme (T4L) and a synthetic peptide catalyst responsible for the selective phosphorylation of the N-acetylglucosamine sugar in a teicoplanin A2-2 derivative. The T4L-Pmh-dPro-Aib-dAla-dAla construct was crystallized in the presence of teicoplanin A2-2. The resulting 2.3 Å resolution protein-peptide-teicoplanin complex cr