A total synthesis of spiruchostatin A

Anticancer efficacy of Spiruchostatin A: current insights into histone deacetylase inhibition and oncologic applications

Spiruchostatin A also referred to as YM753 and OBP801, a cyclic peptide-based natural product derived from Pseudomonas sp., is distinguished by its potent inhibition of Class I histone deacetylases (HDACs). The modulation of epigenetic mechanisms by HDAC inhibitors is fundamental for altering gene expression related to cell growth, apoptosis, and differentiation, highlighting their potential in oncologic therapies. This updated review assesses the antitumor efficacy of Spiruchostatin A across diverse cellular and animal models, scrutinizing its viability as a therapeutic agent against various cancers. A systematic literature review was executed by searching databases such as PubMed/MedLine, Scopus, and Web of Science from October 2022 to February 2023. The inclusion criteria focused on studies involving Spiruchostatin A in the context of cancer treatment, including in vitro and in vivo models. The review concentrated on the compound's mechanistic action, biological activity, and clinical applicability. Spiruchostatin A has demonstrated significant antitumor activities, including inducing apoptosis and inhibiting tumor growth effectively in multiple models. Its therapeutic potential is particularly noted in synergistic applications with other anticancer agents, enhancing its efficacy. Mechanistically, the compound facilitates chromatin relaxation and transcriptional activation of key tumor suppressor genes through increased histone acetylation. Spiruchostatin A exhibits substantial potential as an anticancer agent through effective HDAC inhibition and subsequent epigenetic modifications of cancer cell biology. However, comprehensive clinical trials are imperative to validate its efficacy and safety profiles comprehensively. Future research is warranted to elucidate detailed molecular mechanisms and to develop biomarkers for predicting treatment response. Comprehensive longitudinal clinical studies are also critical to establish Spiruchostatin A's role within the broader oncological therapeutic regimen, along with the exploration of its analogs for improved therapeutic outcomes.

[Synthetic Study on Bicyclic Depsipeptides Containing an Intramolecular Disulfide Bond]

Bicyclic depsipeptide natural products containing an intramolecular disulfide bond are potent histone deacetylase (HDAC) inhibitors. Among them, FK228 (romidepsin) is approved for treating cutaneous T-cell lymphoma and peripheral T-cell lymphoma. This study focused on developing a new synthesis method for producing this class of natural products for use as HDAC inhibitors with high efficacy and low toxicity. In this paper, the total syntheses of FK228 as well as spiruchostatins A and B are described. The synthesis routes include a convergent way to assemble seco-acids via the amide condensation of amine segments with carboxylic acid segments. The syntheses of C4- and C7-modified FK228 analogs (FK-A1 to FK-A8) are also described. The evaluation of HDAC and cell growth inhibitory activities of the synthesized analogs revealed novel aspects of their structure-activity relationship. Potent and highly isoform-selective HDAC1 inhibitors were identified. Furthermore, the analogs showed phosphatidylinositol 3-kinase (PI3K) inhibitory activity. Structural optimization of the analogs as HDAC/PI3K dual inhibitors led to the identification of FK-A11 as the most potent analog.

Depsipeptide synthesis using a late-stage Ag(i)-promoted macrolactonisation of peptide thioamides

Ag(i)-Triggered activation of the thioamide and attack by the C-terminal carboxylate generates an isoimide intermediate that undergoes an intramolecular acyl transfer to furnish the cyclic depsipeptide.

Samarium Iodide-Promoted Asymmetric Reformatsky Reaction of 3-(2-Haloacyl)-2-oxazolidinones with Enals

3-(2-Haloacyl)-2-oxazolidinones were shown to react with enals in an asymmetric SmI₂-promoted Reformatsky reaction to give stereochemically well-defined 3-hydroxy-4-alkenyl- and 3-hydroxy-2-methyl-4-alkenyl imides. Chirality transfer of the Evans (S)-oxazolidinone unit via a Zimmerman-Traxler-like transition state resulted in Reformatsky products with a relative syn-configuration. The absolute configuration of compounds obtained is opposite to the corresponding products obtained via aldol addition of boron enolates to enals using the same Evans oxazolidinones.

Isoform-selective HDAC1/6/8 inhibitors with an imidazo-ketopiperazine cap containing stereochemical diversity

A series of hydroxamic acids linked by different lengths to a chiral imidazo-ketopiperazine scaffold were synthesized. The compounds with linker lengths of 6 and 7 carbon atoms were the most potent in histone deacetylase (HDAC) inhibition, and were specific submicromolar inhibitors of the HDAC1, HDAC6 and HDAC8 isoforms. A docking model for the binding mode predicts binding of the hydroxamic acid to the active site zinc cation and additional interactions between the imidazo-ketopiperazine and the enzyme rim. The compounds were micromolar inhibitors of the MV4-11, THP-1 and U937 cancer cell lines. Increased levels of histone H3 and tubulin acetylation support a cellular mechanism of action through HDAC inhibition.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

Structure-Reactivity Relationships in Lithiated Evans Enolates: Influence of Aggregation and Solvation on the Stereochemistry and Mechanism of Aldol Additions

Aldol additions to isobutyraldehyde and cyclohexanone with lithium enolates derived from acylated oxazolidinones (Evans enolates) are described. Previously characterized trisolvated dimeric enolates undergo rapid addition to isobutyraldehyde to give a 12:1 syn:syn selectivity in high yield along with small amounts of one anti isomer. The efficacy of the addition depends critically on aging effects and the reaction quench. Unsolvated tetrameric enolates that form on warming the solutions are unreactive toward isobutyraldehyde and undergo retroaldol reaction under forcing conditions. Additions to cyclohexanone are relatively slow but form a single isomeric adduct in >80% yield. The ketone-derived aldolates are robust. All attempts to control stereoselectivity by controlling aggregation failed. Rate studies of addition to cyclohexanone trace the lack of aggregation-dependent selectivities to a monomer-based mechanism. The synthetic implications and possible utility of lithium enolates in Evans aldol additions are discussed.

Total synthesis and stereochemical assignment of burkholdac B, a depsipeptide HDAC inhibitor

Three diastereomers of burkholdac B were prepared by total synthesis, enabling the full stereochemical assignment of the natural product. It is proposed that burkholdac B is identical to thailandepsin A independently isolated by Cheng from the same strain of Burkholderia thailandensis . Burkholdac B is the most potent among depsipeptide histone deacetylase inhibitors in growth inhibition of the MCF7 breast cancer cell line with an IC(50) of 60 pM.

Macrolactamization versus macrolactonization: total synthesis of FK228, the depsipeptide histone deacetylase inhibitor

The cyclic depsipeptide FK228 is the only natural product histone deacetylase (HDAC) inhibitor that has advanced to clinical trials as an anticancer agent. While currently obtained by fermentation, total synthesis is an attractive alternative that will facilitate the preparation of unnatural analogues. The previous total syntheses of FK228 featured macrocylization by ester bond formation from a seco-hydroxy acid. Such routes are operationally jeopardized by the steric hindrance of the carboxylic acid and the sensitivity of the allylic alcohol toward elimination. We report a strategically different approach whereby the ester bond is formed intermolecularly at an early stage and macrocyclization is efficiently achieved by amide bond formation.

Total synthesis of the bicyclic depsipeptide HDAC inhibitors spiruchostatins A and B, 5''-epi-spiruchostatin B, FK228 (FR901228) and preliminary evaluation of their biological activity

The bicyclic depsipeptide histone deacetylase (HDAC) inhibitors spiruchostatins A and B, 5''-epi-spiruchostatin B and FK228 were efficiently synthesized in a convergent and unified manner. The synthetic method involved the following crucial steps: i) a Julia-Kocienski olefination of a 1,3-propanediol-derived sulfone and a L- or D-malic acid-derived aldehyde to access the most synthetically challenging unit, (3S or 3R,4E)-3-hydroxy-7-mercaptohept-4-enoic acid, present in a D-alanine- or D-valine-containing segment; ii) a condensation of a D-valine-D-cysteine- or D-allo-isoleucine-D-cysteine-containing segment with a D-alanine- or D-valine-containing segment to directly assemble the corresponding seco-acids; and iii) a macrocyclization of a seco-acid using the Shiina method or the Mitsunobu method to construct the requisite 15- or 16-membered macrolactone. The present synthesis has established the C5'' stereochemistry of spiruchostatin B. In addition, HDAC inhibitory assay and the cell-growth inhibition analysis of the synthesized depsipeptides determined the order of their potency and revealed some novel aspects of structure-activity relationships. It was also found that unnatural 5''-epi-spiruchostatin B shows extremely high selectivity (ca. 1600-fold) for class I HDAC1 (IC(50)=2.4 nM) over class II HDAC6 (IC(50)=3900 nM) with potent cell-growth-inhibitory activity at nanomolar levels of IC(50) values.

Cyclic Disulfides as Functional Mimics of the Histone Deacetylase Inhibitor FK-228

FK-228 is a potent histone deacetylase (HDAC) inhibitor with tremendous therapeutic potential against a wide array of human cancers. We describe the development of analogs that share FK-228's novel mechanism of activation and HDAC inhibition.

Stereoselective Total Synthesis of the Proposed Structure of 2-Epibotcinolide

[Structure: see text] The total synthesis of pseudo 2-epibotcinolide (1b) through several featured synthetic approaches has been attained. First, the chiral linear precursors of the nine-membered ring compound is stereoselectively constructed by the asymmetric aldol reaction for producing beta-hydroxy ester units. Second, the key cyclization reaction to form the nine-membered lactone moiety is efficiently achieved by the extremely facile and powerful mixed-anhydride method promoted by 2-methyl-6-nitrobenzoic anhydride (MNBA) with basic promoters.