Late-stage Diversification Strategy Research Articles

Concise and Stereospecific Total Synthesis of Arenastatin A and Its Segment B Analogs.

A novel and concise synthetic method for arenastatin A, a cytotoxic cyclic depsipeptide of marine origin, was developed in this study. The convergent assembly of the four segments, including the cross-metathesis reaction, gave a cyclization precursor, and Fmoc deprotection caused simultaneous macrocyclization. The Corey-Chaykovsky reaction using a chiral sulfur ylide afforded arenastatin A with complete stereoselectivity in the longest linear sequence of seven reaction steps from the known compound. Using this synthetic method, some analogs of segment B were prepared through a late-stage diversification strategy. The simple SN2 reaction of the thiolate toward the tosylate precursor, prepared using almost the same synthetic method as described above, provided the desired sulfide analogs.

Late-stage diversification strategy for the synthesis of peptide acids and amides using hydrazides

Aim: Modification of the C-terminus of a peptide to improve its properties, particularly after constructing the peptide chain, has great promise in the development of peptide therapeutics. This study discusses the development of a late-stage diversification method for synthesizing peptide acids and amides from hydrazides which can serve as a common precursor. Methods: Peptide hydrazides were synthesized solely by using conventional solid-phase peptide synthesis (SPPS). Hydrazides were subjected to oxidation by potassium peroxymonosulfate (Oxone) to afford carboxylic acids. Azidation of hydrazides using sodium nitrite (NaNO2) under acidic conditions, followed by the addition of β-mercaptoethanol (BME), could also be used to generate carboxylic acids. For the preparation of peptide amides, azides that can be prepared from hydrazides were reacted with ammonium acetate (NH4OAc) or tris(2-carboxyethyl)phosphine (TCEP)∙hydrochloride (HCl) to develop the products through ammonolysis or a Staudinger reaction, which produces iminophosphorane from an azide and a phosphine. The antimicrobial activity of modelin-5 derivatives synthesized from the corresponding hydrazides was evaluated by the colony count of Escherichia coli (E. coli) after treatment with the peptides. Results: Oxone oxidation yielded the corresponding acids rapidly although oxidation-prone amino acids were incompatible. Azidation and subsequent treatment with BME afforded peptide acids an acceptable yield even in sequences containing amino acids that are prone to oxidation. Both methods for conversion of hydrazides to amides were found to afford the desired products in good yield and compatibility. The conditions that were developed were adapted to the synthesis of modelin-5 derivatives from the corresponding hydrazides, yielding late-stage production of the desired peptides. The amides of the resulting peptide showed more potent activity against E. coli than the acid form, and the most potent activity was observed from the hydrazide. Conclusions: The developed protocols allow hydrazides to be converted to acids or amides, enabling late-stage diversification of peptide C-terminal residues.

C-H Glycosylation of Native Carboxylic Acids: Discovery of Antidiabetic SGLT-2 Inhibitors.

C-Glycosides are critical motifs embedded in many bioactive natural products. The inert C-glycosides are privileged structures for developing therapeutic agents owing to their high chemical and metabolic stability. Despite the comprehensive strategies and tactics established in the past few decades, highly efficient C-glycoside syntheses via C-C coupling with excellent regio-, chemo-, and stereoselectivity are still needed. Here, we report the efficient Pd-catalyzed glycosylation of C-H bonds promoted by weak coordination with native carboxylic acids without external directing groups to install various glycals to the structurally diverse aglycon parts. Mechanistic evidence points to the participation of a glycal radical donor in the C-H coupling reaction. The method has been applied to a wide range of substrates (over 60 examples), including many marketed drug molecules. Natural product- or drug-like scaffolds with compelling bioactivities have been constructed using a late-stage diversification strategy. Remarkably, a new potent sodium-glucose cotransporter-2 inhibitor with antidiabetic potential has been discovered, and the pharmacokinetic/pharmacodynamic profiles of drug molecules have been changed using our C-H glycosylation approach. The method developed here provides a powerful tool for efficiently synthesizing C-glycosides to facilitate drug discovery.

Facile and stereospecific synthesis of diverse β-N-glycosyl sulfonamide scaffolds via palladium catalysis.

Glycosylation is an important strategy to improve the druggability of lead compounds. Here, we present a palladium-catalysed stereospecific N-glycosylation of sulfonamides. This approach stands out with wide substrate scope, high functional group tolerance, and easy scalability, furnishing a broad spectrum of densely functionalized β-N-glycosyl sulfonamides with good efficiency and exceptional regio-/stereoselectivity. Diverse drug-like glycosulfonamido scaffolds have been constructed via a late-stage diversification strategy and various facile synthetic transformations of the products. Collectively, the established protocol provides a valuable tool for efficiently preparing glycosyl sulfonamides to facilitate drug discovery.

Late-stage diversification strategy for synthesizing ynamides through copper-catalyzed diynylation and azide-alkyne cycloaddition.

A late-stage diversification strategy for synthesizing ynamides has been developed. This strategy was enabled by the copper-catalyzed direct electrophilic diynylation of sulfonamides with a novel triisopropylsilyl diynyl benziodoxolone, deprotection, and the late-stage chemoselective copper-catalyzed azide-alkyne cycloaddition sequence, which yields various complex molecule-derived ynamides with pyrene, amino acid, nucleoside, and N-acetylglucosamine as substituents.

Bicyclic β-Sheet Mimetics that Target the Transcriptional Coactivator β-Catenin and Inhibit Wnt Signaling.

Protein complexes are defined by the three‐dimensional structure of participating binding partners. Knowledge about these structures can facilitate the design of peptidomimetics which have been applied for example, as inhibitors of protein–protein interactions (PPIs). Even though β‐sheets participate widely in PPIs, they have only rarely served as the basis for peptidomimetic PPI inhibitors, in particular when addressing intracellular targets. Here, we present the structure‐based design of β‐sheet mimetics targeting the intracellular protein β‐catenin, a central component of the Wnt signaling pathway. Based on a protein binding partner of β‐catenin, a macrocyclic peptide was designed and its crystal structure in complex with β‐catenin obtained. Using this structure, we designed a library of bicyclic β‐sheet mimetics employing a late‐stage diversification strategy. Several mimetics were identified that compete with transcription factor binding to β‐catenin and inhibit Wnt signaling in cells. The presented design strategy can support the development of inhibitors for other β‐sheet‐mediated PPIs.

Development of a Late-Stage Diversification Strategy for the 4- and 5-Positions of 4,5,6-Trisubstituted Indazoles.

Indazoles represent a privileged motif in drug discovery. However, the formation of highly substituted indazoles can require the execution of lengthy synthetic routes with minimal opportunities to introduce diversity. In this report, we disclose the development of a late-stage diversification strategy for the 4- and 5-positions of 4,5,6-trisubstituted indazoles. A regioselective C-H functionalization and subsequent nucleophilic aromatic substitution provide two sequential points of diversification. The synthetic sequence delivers rapid access to an array of 4,5,6-trisubstituted indazoles in only four steps from readily available starting materials.

Synthesis and evaluation of designed PKC modulators for enhanced cancer immunotherapy

Bryostatin 1 is a marine natural product under investigation for HIV/AIDS eradication, the treatment of neurological disorders, and enhanced CAR T/NK cell immunotherapy. Despite its promising activity, bryostatin 1 is neither evolved nor optimized for the treatment of human disease. Here we report the design, synthesis, and biological evaluation of several close-in analogs of bryostatin 1. Using a function-oriented synthesis approach, we synthesize a series of bryostatin analogs designed to maintain affinity for bryostatin’s target protein kinase C (PKC) while enabling exploration of their divergent biological functions. Our late-stage diversification strategy provides efficient access to a library of bryostatin analogs, which per our design retain affinity for PKC but exhibit variable PKC translocation kinetics. We further demonstrate that select analogs potently increase cell surface expression of CD22, a promising CAR T cell target for the treatment of leukemias, highlighting the clinical potential of bryostatin analogs for enhancing targeted immunotherapies.

Late-Stage Diversification of Phosphinic Dehydroalanine Pseudopeptides Based on a Giese-Type Radical C-Alkylation Strategy.

A straightforward, late-stage diversification strategy for the installation of side chains on readily accessible unsaturated phosphinopeptidic scaffolds based on a Giese-type addition of alkyl radicals has been investigated. Among different alternatives, the preferred methodology is operationally simple as it can be carried out in an open flask with no need for protection of acidic moieties. Direct application to the synthesis of SPPS-compatible building blocks or to longer peptides is also reported.

Chiral-pool synthesis of 1,2,4-trisubstituted 1,4-diazepanes as novel σ1 receptor ligands

Starting from enantiomerically pure amino acids, 1,4-diazepanes with various substituents in 1, 2, and 4-position were synthesized following the late stage diversification strategy. The key step in the formation of the seven-membered ring was the intramolecular EDC coupling of amino acids 15, 26, and 39. The configuration in 2-position does not influence the σ1 affinity and selectivity over related receptors. A cyclohexylmethyl or a butyl group are the preferred substituents in 4-position, whereas a methyl moiety in 2-position and a (substituted) benzyl moiety in 1-position result in the highest σ1 affinity. These results fit nicely to the reported σ1 pharmacophore models. The compounds did not inhibit the structurally related fungal enzyme sterol Δ8,7-isomerase, but showed inhibition of diverse enzymes in late cholesterol biosynthesis at high concentrations. In a screening against more than 50 target proteins, (2S)-1-benzyl-4-(4-methoxybenzyl)-2-methyl-1,4-diazepane ((S)-28b, Ki(σ1)=0.86nM) showed a clean receptor profile. The dose dependent potentiation of electrically stimulated contractions of guinea pig vas deferens indicates σ1 agonistic activity of (S)-28b. Even at a dose of 100mg/kg (S)-28b did not induce severe toxic or behavioral effects in the Irwin screen. Clear cognition enhancing effects were observed for (S)-28b after inducing amnesia by scopolamine.

Discovery of Potent Antivirals against Amantadine-Resistant Influenza A Viruses by Targeting the M2-S31N Proton Channel.

Despite the existence of flu vaccines and small-molecule antiviral drugs, influenza virus infection remains a public health concern that warrants immediate attention. As resistance to the only orally bioavailable drug, oseltamivir, has been continuously reported, there is a clear need to develop the next-generation of anti-influenza drugs. We chose the influenza A virus M2-S31N mutant proton channel as the drug target to address this need as it is one of the most conserved viral proteins and persist in >95% of currently circulating influenza A viruses. In this study, we report the development of a late-stage diversification strategy for the expeditious synthesis of M2-S31N inhibitors. The channel blockage and antiviral activity of the synthesized compounds were tested in two-electrode voltage clamp assays and antiviral assays, respectively. Several M2-S31N inhibitors were identified to have potent M2-S31N channel blockage and micromolar antiviral efficacy against several M2-S31N-containing influenza A viruses.

Preparation of Fluorescent Microcystin Derivatives by Direct Arginine Labelling and Their Biological Evaluation.

Microcystin is the most prevalent toxin produced by cyanobacteria and poses a severe threat to livestock, humans and entire ecosystems. We report the preparation of a series of fluorescent microcystin derivatives by direct arginine labelling of the unprotected peptides at the guanidinium side chain. This new method allows a simple late-stage diversification strategy for native peptides devoid of protecting groups under mild conditions. A series of fluorophores were conjugated to microcystin-LR in good to very good yield. The fluorescent probes displayed biological activity comparable to that of unlabelled microcystin, in both phosphatase inhibition assays and toxicity tests on the crustacean Thamnocephalus platyurus. In addition, we demonstrate that the fluorescent probes penetrated Huh7 cells. Whole-animal imaging was performed on T. platyurus: labelled compound was mainly observed in the digestive tract.

Synthesis of Thiophene-Based TAK-779 Analogues by C–H Arylation

A rapid synthesis of thiophene-based TAK-779 analogues 1 is reported using a late-stage diversification strategy. At the end of the synthesis, the key building block 2, which was prepared in six steps from thiophene, was arylated regioselectively at the α-position directly with iodoarenes. Since 2 offers several reactive positions, various established catalyst systems were tested. It was found that Crabtree catalyst (an Ir catalyst) converted efficiently and selectively the thiophene system 2 into 2-aryl-substituted compounds 9. The direct C-H arylation of 2 with electron-rich iodoarenes led to high yields, whereas electron-deficient iodoarenes required longer reaction times for complete conversion. A small set of diverse amides 1 was synthesized by hydrolysis of 9 and subsequent HATU coupling with primary amines 4.

Total synthesis and biological evaluation of a series of macrocyclic hybrids and analogues of the antimitotic natural products dictyostatin, discodermolide, and taxol.

The design, synthesis, and biological evaluation of a series of hybrids and analogues of the microtubule-stabilizing anticancer agents dictyostatin, discodermolide, and taxol is described. A 22-membered macrolide scaffold was prepared by adapting earlier synthetic routes directed towards dictyostatin and discodermolide, taking advantage of the distinctive structural and stereochemical similarities between these two polyketide-derived marine natural products. Initial endeavors towards accessing novel discodermolide/dictyostatin hybrids led to the adoption of a late-stage diversification strategy and the construction of a small library of methyl-ether derivatives, along with the first triple hybrids bearing the side-chain of taxol or taxotere attached through an ester linkage. Biological assays of the anti-proliferative activity of these compounds in a series of human cancer cell lines, including the taxol-resistant NCI/ADR-Res cell line, allowed the proposal of various structure-activity relationships. This led to the identification of a potent macrocyclic discodermolide/dictyostatin hybrid 12 and its C9 methoxy derivative 38, accessible by an efficient total synthesis and with a similar biological profile to dictyostatin.

Synthesis and biological evaluation of novel analogues of dictyostatin

Novel analogues of the microtubule-stabilising agent dictyostatin were designed using existing SAR information from the structurally related discodermolide, synthesised by a late-stage diversification strategy and evaluated in vitro for growth inhibition against a range of human cancer cell lines, including those known to exhibit Taxol-resistance (AsPC-1, DLD-1, PANC-1, NCI/ADR).

Design, synthesis and biological evaluation of novel, simplified analogues of laulimalide: modification of the side chain

Novel, simplified analogues of the microtubule-stabilizing anticancer agent laulimalide, including the first derivatives with unnatural side chains, were designed by molecular modelling, synthesized by a late-stage diversification strategy, and evaluated in vitro for growth inhibition of human ovarian carcinoma cell lines (A2780, A2780/AD10).

Identification of a Tunable Site in Bryostatin Analogs: C20 Bryologs through Late Stage Diversification

[structure: see text] The C20 region of our bryostatin analogs was identified as a nonpharmacophoric site that could be varied to tune analogs for function and physical properties without significantly affecting their binding affinity for PKC. The use of this site in a late-stage diversification strategy has enabled the facile synthesis of a variety of new C20 analogs, all of which retain nanomolar affinity for PKC, in agreement with our pharmacophore hypothesis.