Total synthesis of TAK-kinase inhibitor LL-Z1640-2 via consecutive macrocyclization and transannular aromatization

A Convergent Approach to Resorcinolic Macrolides to Expand Structural Diversity

The resorcinolic macrolide (RM) family comprises over 50 natural products with diverse biological activities, including the potent natural Hsp90 inhibitor radicicol. Here, we report a modular and enantioselective synthetic strategy featuring a biomimetic macrocyclization-aromatization cascade that enables rapid access to natural and unnatural RMs. Using this route, we generated a small panel of minimal RMs, introducing covalent warheads, double bonds for macrocycle rigidification, and modifications at the C15 position, a position that has not been modified before. We also synthesized macrocyclic peptide-RM hybrids, offering a platform for rapid diversification. We evaluated all analogs for inhibitory activity against Hsp90α and Hsp90β and for disruption of the KRasG12C-CRAF protein-protein interaction (PPI). We found that introduction of polar groups at C15 improved Hsp90 activity relative to the representative RM de-O-methyllasiodiplodin, dependent on stereochemistry, whereas introduction of larger groups at C15 or introduction of a trans double bond into the macrocycle reduced activity. Two analogs with poor Hsp90 inhibitory activity exhibited dose-dependent inhibition of the KRasG12C-CRAF PPI. This work demonstrates that strategic modifications of a minimal RM scaffold through modular chemical insight can provide foundational structure-activity relationships for the class.

Chemical inhibition of TRAF6-TAK1 axis as therapeutic strategy of endotoxin-induced liver disease

The liver is exposed to gut-derived bacterial endotoxin via portal circulation, and recognizes it through toll-like receptor 4 (TLR4). Endotoxin lipopolysaccharide (LPS) stimulates the self-ubiquitination of ubiquitin ligase TRAF6, which is linked to scaffold with protein kinase TAK1 for auto-phosphorylation and subsequent activation. TAK1 activity is a signal transducer in the activating pathways of transcription factors NF-κB and AP-1 for production of various cytokines. Here, we hypothesized that TRAF6-TAK1 axis would be implicated in endotoxin-induced liver disease. Following exposure to endotoxin LPS, TLR4-mediated phosphorylation of TAK1 and transcription of cell-death cytokine TNF-α were triggered in Kupffer cells but not in hepatocytes as well as TNF receptor-mediated and caspase-3-executed apoptosis was occurred in D-galactosamine (GalN)-sensitized hepatocytes under co-culture with Kupffer cells. Treatment with pyridinylmethylene benzothiophene (PMBT) improved endotoxin LPS-induced hepatocyte apoptosis in GalN-sensitized C57BL/6 mice via suppressing NF-κB- and AP-1-regulated expression of TNF-α in Kupffer cells, and rescued the mice from hepatic damage-associated bleeding and death. As a mechanism, PMBT directly inhibited Lys 63-linked ubiquitination of TRAF6, and mitigated scaffold assembly between TRAF6 and the TAK1-activator adaptors TAB1 and TAB2 complex in Kupffer cells. Thereby, PMBT interrupted TRAF6 ubiquitination-induced activation of TAK1 activity in the TLR4-mediated signal cascade leading to TNF-α production. However, PMBT did not directly affect the apoptotic activity of TNF-α on GalN-sensitized hepatocytes. Finally, we propose chemical inhibition of TRAF6-TAK1 axis in Kupffer cells as a strategy for treating liver disease due to gut-derived endotoxin or Gram-negative bacterial infection.

Natural and Synthetic Lactones Possessing Antitumor Activities

Cancer is one of the leading causes of death globally, accounting for an estimated 8 million deaths each year. As a result, there have been urgent unmet medical needs to discover novel oncology drugs. Natural and synthetic lactones have a broad spectrum of biological uses including anti-tumor, anti-helminthic, anti-microbial, and anti-inflammatory activities. Particularly, several natural and synthetic lactones have emerged as anti-cancer agents over the past decades. In this review, we address natural and synthetic lactones focusing on their anti-tumor activities and synthetic routes. Moreover, we aim to highlight our journey towards chemical modification and biological evaluation of a resorcylic acid lactone, L-783277 (4). We anticipate that utilization of the natural and synthetic lactones as novel scaffolds would benefit the process of oncology drug discovery campaigns based on natural products.

Asymmetric total syntheses of naturally occurring α,β-enone-containing RALs, L-783290 and L-783277 through intramolecular base-mediated macrolactonization reaction

Asymmetric total synthesis of two naturally occurring α,β-enone containing RALs, L-783290 and L-783277 is described in this article. An E-selective Horner-Wadsworth-Emmons (HWE) olefination was used as a key reaction to construct the C7'-C8' olefinic unsaturation in L-783290. An enantiopure alkyne addition to the aldehyde followed by Z-selective partial reduction was employed to construct the C7'-C8' olefinic unsaturation in L-783277. Biomimetic lactonization reaction was used to construct the macrolactone core in both the target molecules.

A Concise and Stereoselective Total Synthesis of Paecilomycin E

A concise approach for the first total synthesis of paecilomycin E is described involving Alder-Rickert reaction, Mitsunobu esterification and ring closing metathesis as the key steps. This approach has successfully demonstrated the Alder-Rickert protocol for the construction of resorcylic acid unit.

Resorcylic acid lactones (RALs) and their structural congeners: recent advances in their biosynthesis, chemical synthesis and biology

Resorcylic acid lactones (RALs) are naturally occurring 14-membered macrolactones that constitute a class of polyketides derived from fungal metabolites and that possess significant and promising biological activity.

Total Syntheses of Anti-HIV Cyclodepsipeptides Aetheramides A and B

A concise total synthesis of aetheramide A in an overall yield of 4.7% with a longest linear sequence of 15 steps is described. This synthetic strategy features macrocyclization via an intramolecular trapping of acylketene generated from dioxinone precursor, and stereoselective late-stage methylation of β-ketoamide. Aetheramide B could be synthesized via the ester migration of aetheramide A.

Penicillanthone and penicillidic acids A–C from the soil-derived fungus Penicillium aculeatum PSU-RSPG105

A new xanthone (penicillanthone, 1) and three new diphenyl ether derivatives (penicillidic acids A–C, 2–4) together with 14 known compounds (5–18) were isolated from the soil-derived fungus Penicillium aculeatum PSU-RSPG105.

β-Keto-dioxinones and β,δ-diketo-dioxinones in biomimetic resorcylate total synthesis

Resorcylates are a large group of bioactive natural products that are biosynthesized from acetate and malonate units via the intermediacy of polyketides. These polyketides undergo cyclization reactions to introduce the aromatic core. The bioactivities of the resorcylates including resorcylate macrocyclic lactones include anticancer, antimalarial, mycotoxicity, antifungal, and antibiotic properties, and several compounds in the series are already in use in medicine. Examples are prodrugs derived from mycophenolic acid as immunosuppressants and the Hsp-90 inhibitor, AT13387, which is in phase-II clinical trials for the treatment of small cell lung cancer and melanoma. In consequence of these biological activities, methods for the concise synthesis of diverse resorcylates are of considerable importance. In natural product chemistry, biomimetic total synthesis can have significant advantages including functional group tolerance in key steps, the minimization of the use of protection and deprotection reactions and the shortening of the total number of synthetic steps. This Account provides a description of our adaption of the dioxinone chemistry of Hyatt, Clemens, and Feldman for the synthesis and retro-Diels-Alder reactions of diketo-dioxinones. Such dioxinones, which were synthesized by a range of C-acylation reactions, were found to undergo retro-Diels-Alder reactions on heating to provide the corresponding triketo-ketenes with the loss of acetone. The ketene reactive intermediates were rapidly trapped both inter- and intramolecularly with alcohols to provide the corresponding β,δ,ζ-triketo-esters. These compounds, which consist of keto-enol mixtures, readily undergo cycloaromatization to produce resorcylate esters and macrocyclic lactones. We have established the use of diketo-dioxinones as key general intermediates for the synthesis of diverse resorcylate natural products and for the synthesis of new classes of compounds for the generation of medicinal chemistry lead structures. Many of the methods used were found to be tolerant of multiple sensitive functional groups. These include enolate C-acylations with acyl chlorides, 1-acyl-benzotriazoles, acyl imidazolides, or Weinreb amides to prepare diketo-dioxinones and their subsequent use to prepare β,δ,ζ-triketo-esters and lactones and hence resorcylates. In addition, in most cases, phenol protection was avoided. As an alternative to the synthesis of β,δ,ζ-triketo-esters, diketo-dioxinones were also found to undergo cycloaromatization with retention of the ketal entity via a nonketene pathway. Finally, diketo-dioxinones with an allyl, prenyl, geranyl, or other 2-alkenyl carboxylate esters at the γ-carbon underwent decarboxylative rearrangement with tetrakis(triphenylphosphine)palladium catalysis to produce α-substituted diketo-dioxinones and resorcylates with 3-allyl, prenyl, geranyl, or other 2-alkenyl groups. Such diketo-dioxinone chemistry was used in the total synthesis of natural products including aigialomycin, cruentaren A, and the oligomeric resorcylate antibiotics ent-W1278 A, B, and C. Additionally, tandem use of the decarboxylative rearrangement process and cycloaromatization was used in the total synthesis of natural products including the methyl ester of cristatic acid, mycophenolic acid, and hongoquercin B. The methodology was also applied to the synthesis of 9,10-anthraquinones, o-aminoalkyl resorcylates, dihydroxyisoindolinones, oligomers, and resorcinamides. The development of this methodology is described in this Account, showcasing its applicability and versatility for the synthesis of complex resorcylate products.

Modular total syntheses of the marine-derived resorcylic Acid lactones cochliomycins a and B using a late-stage nozaki-hiyama-kishi macrocyclization reaction

The natural products cochliomycin A (1) and cochliomycin B (2), two resorcylic acid lactones obtained from marine sources, have been prepared in a concise and stereocontrolled manner from the readily accessible building blocks 4-6. Olefin cross-metathesis, trans-esterification and Nozaki-Hiyama-Kishi (NHK) macrocyclization reactions were employed in the key steps. Hydrolysis of the immediate precursor to cochliomycin B affords the resorcylic acid lactone zeaenol (24).

The taumycin A macrocycle: asymmetric total synthesis and revision of relative stereochemistry

The first asymmetric total synthesis and revision of the relative configuration of the 12-membered taumycin A macrocycle is described. Key to the success of this work was a novel α-keto ketene macrocyclization that provided an efficient means by which to access two diastereomers of the desired macrolide without the need to employ additional coupling agents or unnecessary oxidation state adjustments.

Asymmetric total synthesis of paecilomycin E, 10'-epi-paecilomycin E and 6'-epi-cochliomycin C

The asymmetric total syntheses of naturally occurring resorcylic acid lactone paecilomycin E and two of its structural congeners have been reported in this article. The major highlight of the synthetic venture is the application of the late stage Mitsunobu macrolactonization method (as it is difficult to achieve the desired products through the standard carboxyl activation method) of a properly functionalized seco-acid. The macrolactonization precursor was synthesized by applying an "E"-selective Julia-Kocienski olefination of a highly functionalized aromatic aldehyde and a sulphone, which constitutes all the stereocenters (C4', C5', C6' and C10'; 3S,7R,8R,9S) in the target molecule.