Simple one-flask method for the preparation of hydroxamic acids

Hydroxamic Acid Derivatives: From Synthetic Strategies to Medicinal Chemistry Applications

Since the approval of three hydroxamic acid-based HDAC inhibitors as anticancer drugs, such functional groups acquired even more notoriety in synthetic medicinal chemistry. The ability of hydroxamic acids (HAs) to chelate metal ions makes this moiety an attractive metal binding group-in particular, Fe(III) and Zn(II)-so that HA derivatives find wide applications as metalloenzymes inhibitors. In this minireview, we will discuss the most relevant features concerning hydroxamic acid derivatives. In a first instance, the physicochemical characteristics of HAs will be summarized; then, an exhaustive description of the most relevant methods for the introduction of such moiety into organic substrates and an overview of their uses in medicinal chemistry will be presented.

Hydroxamic Acid: An Underrated Moiety? Marrying Bioinorganic Chemistry and Polymer Science

Even 150 years after their discovery, hydroxamic acids are mainly known as the starting material for the Lossen rearrangement in textbooks. However, hydroxamic acids feature a plethora of existing and potential applications ranging from medical purposes to materials science, based on their excellent complexation properties. This underrated functional moiety can undergo a broad variety of organic transformations and possesses unique coordination properties for a large variety of metal ions, for example, Fe(III), Zn(II), Mn(II), and Cr(III). This renders it ideal for biomedical applications in the field of metal-associated diseases or the inhibition of metalloenzymes, as well as for the separation of metals. Considering their chemical stability and reactivity, their biological origin and both medical and industrial applications, this Perspective aims at highlighting hydroxamic acids as highly promising chelators in the fields of both medical and materials science. Furthermore, the state of the art in combining hydroxamic acids with a variety of polymer structures is discussed and a perspective regarding their vast potential at the interface of bioinorganic and polymer chemistry is given.

Formamide catalyzed activation of carboxylic acids - versatile and cost-efficient amidation and esterification

Formamide catalysis enables highly cost-efficient amide C–N and ester C–O bond formation through carboxylic acid chlorides as essential intermediates.

A novel, broadly applicable method for amide C–N and ester C–O bond formation is presented based on formylpyrrolidine (FPyr) as a Lewis base catalyst. Herein, trichlorotriazine (TCT), which is the most cost-efficient reagent for OH-group activation, was employed in amounts of ≤40 mol% with respect to the starting material (100 mol%). The new approach is distinguished by excellent cost-efficiency, waste-balance (E-factor down to 3) and scalability (up to >80 g). Moreover, high levels of functional group compatibility, which includes acid-labile acetals and silyl ethers, are demonstrated and even peptide C–N bonds can be formed. In comparison to reported amidation procedures using TCT, yields are considerably improved (for instance from 26 to 91%) and esterification is facilitated for the first time in synthetically useful yields. These significant enhancements are rationalized by activation by means of acid chlorides instead of less electrophilic acid anhydride intermediates.

Methods for Hydroxamic Acid Synthesis

Substituted hydroxamic acid is one of the most extensively studied pharmacophores because of their ability to chelate biologically important metal ions to modulate various enzymes, such as HDACs, urease, metallopeptidase, and carbonic anhydrase. Syntheses and biological studies of various classes of hydroxamic acid derivatives have been reported in numerous research articles in recent years but this is the first review article dedicated to their synthetic methods and their application for the synthesis of these novel molecules. In this review article, commercially available reagents and preparation of hydroxylamine donating reagents have also been described.

A General Catalytic Method for Highly Cost- and Atom-Efficient Nucleophilic Substitutions

A general formamide-catalyzed protocol for the efficient transformation of alcohols into alkyl chlorides, which is promoted by substoichiometric amounts (down to 34 mol %) of inexpensive trichlorotriazine (TCT), is introduced. This is the first example of a TCT-mediated dihydroxychlorination of an OH-containing substrate (e.g., alcohols and carboxylic acids) in which all three chlorine atoms of TCT are transferred to the starting material. The consequently enhanced atom economy facilitates a significantly improved waste balance (E-factors down to 4), cost efficiency, and scalability (>50 g). Furthermore, the current procedure is distinguished by high levels of functional-group compatibility and stereoselectivity, as only weakly acidic cyanuric acid is released as exclusive byproduct. Finally, a one-pot protocol for the preparation of amines, azides, ethers, and sulfides enabled the synthesis of the drug rivastigmine with twofold S_N 2 inversion, which demonstrates the high practical value of the presented method.

N-hydroxy-substituted 2-aryl acetamide analogs: A novel class of HIV-1 integrase inhibitors

An in silico method has been used to discover N-hydroxy-substituted 2-aryl acetamide analogs as a new class of HIV-1 integrase inhibitors. Based on the molecular requirements of the binding pocket of catalytic active site, two molecules (compounds 2 and 4b) were designed as fragments. These were further synthesized and biologically evaluated. In vitro potency along with docking studies highlighted compound 4b as an active fragment which was further used to synthesize new leads as HIV-1 integrase inhibitors. Finally, six promising compounds (compounds 5b, 5c, 5e, 6-2c, 6-3b, and 6-5b) were identified by integrase inhibition assay (>50% inhibition). Based on in vitro anti-HIV-1 activity in a reporter gene-based cell assay system, compounds 5d, 6s, and 6k were found as novel HIV-1 integrase inhibitors due to its better selectivity index. Additionally, docking study revealed the importance of H-bond as well as hydrophobic interactions with Asn155, Lys156, and Lys159 which were required for their anti-HIV-1 activity.

Photoorganocatalytic One-Pot Synthesis of Hydroxamic Acids from Aldehydes

An efficient one-pot synthesis of hydroxamic acids from aldehydes and hydroxylamine is described. A fast, visible-light-mediated metal-free hydroacylation of dialkyl azodicarboxylates was used to develop the subsequent addition of hydroxylamine hydrochloride. A range of aliphatic and aromatic aldehydes were employed in this reaction to give hydroxamic acids in high to excellent yields. Application of the current methodology was demonstrated in the synthesis of the anticancer medicine vorinostat.

An efficient mechanochemical synthesis of amides and dipeptides using 2,4,6-trichloro-1,3,5-triazine and PPh3

A mechanochemical method for amidation of carboxylic acids and urethane-protected (Fmoc, Cbz, Boc) α-amino acids has been developed as a facile, efficient, and eco-friendly route toward amides and dipeptides.

Diorganotin(IV) derivatives of N-methyl p-fluorobenzo-hydroxamic acid: preparation, spectral characterization, X-ray diffraction studies and antitumor activity

Three diorganotin(IV) complexes of the general formula R₂Sn[RcC(O)N(RN)O] (Rc = aryl, RN = Alkyl) have been synthesized by refluxing in toluene the corresponding diorganotin(IV) oxides with the free ligand N-methyl p-fluorobenzohydroxamic acid, using a Dean and Stark water separator. The ligand was derived from the reaction of the corresponding p-fluorobenzoyl chloride and N-methylhydroxylamine hydrochloride in the presence of sodium hydrogen carbonate. The isolated free ligand and its respective diorganotin compounds have been characterized by elemental analysis, IR and ¹H-, ¹³C-, ¹¹⁹Sn-NMR spectroscopies. The crystal structures of the diorganotin complexes have been confirmed by single crystal X-ray diffraction methods. The investigations carried out on the diorganotin(IV) complexes of N-methyl p-fluorobenzohydroxamic acid confirmed a 1:2 stoichiometry. The complex formation took place through the O,O-coordination via the carbonyl oxygen and subsequent deprotonated hydroxyl group to the tin atom. The crystal structures of three diorganotin complexes were determined and were found to adopt six coordination geometries at the tin centre with coordination to two ligand moieties.

Targeting metalloproteins by fragment-based lead discovery

It has been estimated that nearly one-third of functional proteins contain a metal ion. These constitute a wide variety of possible drug targets including metalloproteinases, dehydrogenases, oxidoreductases, hydrolases, deacetylases, or many others in which the metal ion is either of catalytic or of structural nature. Despite the predominant role of a metal ion in so many classes of drug targets, current high-throughput screening techniques do not usually produce viable hits against these proteins, likely due to the lack of proper metal-binding pharmacophores in the current screening libraries. Herein, we describe a novel fragment-based drug discovery approach using a metal-targeting fragment library that is based on a variety of distinct classes of metal-binding groups designed to reliably anchor the fragments at the target's metal ions. We show that the approach can effectively identify novel, potent and selective agents that can be readily developed into metalloprotein-targeted therapeutics.

Hypervalent iodine(III)-mediated oxidation of aldoximes to N-acetoxy or N-hydroxy amides

Treatment of various aliphatic and aromatic aldoximes with the hypervalent iodine(iii) reagents (diacetoxyiodo)benzene (DIB) or Koser's reagent [hydroxy(tosyloxy)iodo]benzene (HTIB) gave, respectively, N-acetoxy or N-hydroxy amides in good yields rather than the expected nitrile oxide dimerised product oxadiazole-N-oxides reported to be formed with other oxidising and hypervalent iodine reagents. The acetate or the hydroxyl group of DIB or HTIB attacks on the aryl/alkylnitrile oxides formed in situ, which, upon intramolecular rearrangement, gave the expected N-acetoxy or N-hydroxy amides.

Histone deacetylase and microtubules as targets for the synthesis of releasable conjugate compounds

Design and synthesis of an HDAC inhibitor and its merger with three tubulin binders to create releasable conjugate compounds is described. The biological evaluation includes: (a) in vitro reactivity with glutathione, (b) antiproliferative activity, (c) cell cycle analysis and (d) quantification of protein acetylation. The cellular pharmacology study indicated that the HDAC-inhibitor-drug conjugates retained antimitotic and proapoptotic activity with a reduced potency.

A peptide hydroxamate library for enrichment of metalloproteinases: towards an affinity-based metalloproteinase profiling protocol

A compound library of 96 enantiopure N-terminal succinyl hydroxamate functionalized peptides was synthesized on solid phase. All compounds were tested for their inhibitory potential towards MMP-9, MMP-12 and ADAM-17, which led to the identification of both broad spectrum inhibitors and metalloproteinase-selective ones. Eight potent and less potent inhibitors were immobilized on Sepharose beads and evaluated in solid-phase enrichment of active MMP-9, MMP-12 and ADAM-17. In addition, one of these inhibitors was used for solid-phase enrichment of endogenous ADAM-17 from a complex proteome (a lysate prepared from cultured A549 cells).