The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

AJICAP-M: Traceless Affinity Peptide Mediated Conjugation Technology for Site-Selective Antibody-Drug Conjugate Synthesis

A traceless site-selective conjugation method, "AJICAP-M", was developed for native antibodies at sites using Fc-affinity peptides, focusing on Lys248 or Lys288. It produces antibody-drug conjugates (ADCs) with consistent drug-to-antibody ratios, enhanced stability, and simplified manufacturing. Comparative in vivo assessment demonstrated AJICAP-M's superior stability over traditional ADCs. This technology has been successfully applied to continuous-flow manufacturing, marking the first achievement in site-selective ADC production. This manuscript outlines AJICAP-M's methodology and its effectiveness in ADC production.

Oxidative hydrolysis of aliphatic bromoalkenes: scope study and reactivity insights

We have developed an operationally simple method for the synthesis of dialkyl α-bromoketones from bromoalkenes by utilizing a hypervalent iodine-catalyzed oxidative hydrolysis reaction. This catalytic process provides both symmetrical and unsymmetrical dialkyl bromoketones with moderate yields across a broad range of bromoalkene substrates. Our studies also reveal the formation of Ritter-type side products by an alternative reaction pathway.

Fabrication of a novel magnetic nanostructure based on cellulose-gellan gum hydrogel, embedded with MgAl LDH as an efficient catalyst for the synthesis of polyhydroquinoline derivatives

Nanocatalysts play a vital role in chemical reactions, energy conservation, and pollution control. They significantly contribute to organic synthesis by using natural polymers as nanoparticle substrates in nanocatalysts. Natural hydrogels made from polysaccharide and/or protein sources may be used to accomplish this. Recent research has focused on using layered double-hydroxides (LDHs) in composites having catalytic properties. Magnetic features of the catalyst allow its extraction from the environment using a magnet after the reaction, improving product efficiency. This work developed a catalyst for producing physiologically relevant polyhydroquinoline derivatives using a novel magnetic nanocomposite containing natural cellulose-gellan gum hydrogel and MgAl LDH. The Cell-GG hydrogel/MgAl LDH/Fe3O4 nanocomposite showed over 90 % efficiency in one-pot production of polyhydroquinoline derivatives by asymmetric Hantzsch condensation. Dimedone, ammonium acetate, ethyl acetoacetate, and different substituted aldehydes were employed in successive processes to create polyhydroquinoline derivatives. High product efficiency, quick reaction time, room temperature functioning, and easy separation with a magnet suggest a potent catalyst. Interestingly, the catalyst retains 80 % of its original capability after four cycles. Additionally, the Cell-GG hydrogel/MgAl LDH/Fe3O4 nanocomposite was analyzed using several methods, including FT-IR, FE-SEM, EDX, XRD, VSM and TGA, to obtain insight into its chemical and physical characteristics.

Photocatalytic Radical Coupling of Organoborates with α-Halogenated Electron-Poor Olefins

Herein, we report the visible-light-mediated addition of organoborates to α-halogenated electron-poor olefins enabled by an environmentally benign metal-free catalyst. The method accommodates a variety of boronic acid derivatives as well as alkenes and delivers the corresponding saturated α-halo-derivatives in up to 90% yields. The obtained products are high-value building blocks in organic synthesis, allowing for a variety of follow-up transformations.

Bispecific Antibodies Produced via Chemical Site-Specific Conjugation Technology: AJICAP Second-Generation

Bispecific antibodies (BisAbs) are biotherapeutics that amalgamate the specificities of two distinct antibodies into one molecule, however, their engineering requires genetic modification and remains time-consuming. Therefore, we used AJICAP second-generation technology, which drives the production of site-specific conjugation without genetic modification requirements, to generate BisAbs. Using haloketone chemistry as an alternative to maleimide chemistry, we successfully produced site-specific antibody conjugates. Pharmacokinetic studies revealed that the haloketone-based antibody conjugate was stable in the rat plasma. The resultant BisAbs were rigorously evaluated, and surface plasmon resonance measurements and flow cytometry analyses confirmed that the antigen binding remained intact. Additionally, the affinity for the neonatal Fc receptor (FcRn) was retained after conjugation. Further cytotoxicity evaluation emphasized the pronounced activity of the generated BisAbs. This novel approach introduces a fully chemical, site-specific strategy capable of producing BisAbs, heralding a new era in the field of biotherapeutics.

Rapid and General Access to α-Haloketones Using Quaternary Ammonium Salts as Halogen Sources

A general, rapid, and scalable method for the preparation of α-halogenated ketones using N-alkenoxypyridinium salts as substrates and quaternary ammonium salts as halogen sources was developed, featuring mild reaction conditions, excellent functional group tolerance, short reaction times, and a wide substrate scope.

Tail-approach based design, synthesis, and cytotoxic evaluation of novel disubstituted and trisubstituted 1,3-thiazole benzenesulfonamide derivatives with suggested carbonic anhydrase IX inhibition mechanism

A novel series of 2,4,5- and 2,3,4-trisubstituted thiazole hybrids with 1,3,4-thiadiazolylbenzenesulfonamide was designed following the tail approach as possible hCAIX inhibitors. The key intermediate 1 was condensed with thiosemicarbazide 2a to give 1,3,4-thiadiazolylthiosemicarbazone 3, which upon hetero-cyclization with substituted α-haloketones and esters afforded 2,4,5-trisubstituted thiazole-1,3,4-thiadiazole conjugates 4-8. Furthermore, the trisubstituted thiazole-1,3,4-thiadiazole hybrids 12a-d were synthesized via the regioselective cyclization of 4-substituted-1,3,4-thiadiazolylthiosemicarbazones with phenacyl bromide. The cyclized 2,4-disubstituted thiazole 4 enhanced cytotoxicity by nine, four and two times against HepG-2, Caco2, and MCF-7, respectively. Moreover, the simple methyl substitution on the thiosemicarbazone terminus 9a improved the parent derivative 3 cytotoxicity by nine, fourteen, and six times against HepG-2, Caco2, and MCF-7, respectively. This astonishing cytotoxicity was elaborated with hCAIX molecular docking simulation of 4, 9a, and 12d demonstrating binding to zinc and its catalytic His94. Furthermore, molecular dynamic simulation 9a revealed stable hydrogen bonding with hCAIX with interaction energy of -61.07 kcal mol-1 and ΔGbinding MM-PBSA of -9.6 kcal mol-1.

Merging Cu(I) and Cu(II) Photocatalysis: Development of a Versatile Oxohalogenation Protocol for the Sequential Cu(II)/Cu(I)-Catalyzed Oxoallylation of Vinylarenes

A sequential photocatalytic strategy is developed via the merger of Cu(II)/Cu(I)-catalytic cycles for the oxoallylation of vinyl arenes via α-haloketones. The initial Cu(II)-photocatalyzed oxohalogenation exploits ligand-to-metal charge transfer (LMCT) to generate halide radicals from acyl halides utilizing air as a terminal oxidant and can be employed for the late-stage modification of pharmaceuticals and agrochemicals. α-Bromoketones obtained this way can be subsequently subjected to a one-pot Cu(I)-photocatalyzed allylation. This sequential photocatalysis proceeds in a highly regio- and chemoselective fashion and is inconsequential to the electronic nature of styrenes.

Novel formats of antibody conjugates: recent advances in payload diversity, conjugation, and linker chemistry

INTRODUCTION

In the field of bioconjugates, the focus on antibody - drug conjugates (ADCs) with novel payloads beyond the traditional categories of potent cytotoxic agents is increasing. These innovative ADCs exhibit various molecular formats, ranging from small-molecule payloads, such as immune agonists and proteolytic agents, to macromolecular payloads, such as oligonucleotides and proteins.

AREAS COVERED

This review offers an in-depth exploration of unconventional strategies for designing conjugates with novel mechanisms of action and notable examples of approaches that show promising prospects. Representative examples of novel format payloads and their classification, attributes, and appropriate conjugation techniques are discussed in detail.

EXPERT OPINION

The existing basic technologies used to manufacture ADCs can be directly applied to synthesize novel formatted conjugates. However, a wide variety of new payloads require the creation of customized technologies adapted to the unique characteristics of these payloads. Consequently, fundamental technologies, such as conjugation methods aimed at achieving high drug - antibody ratios and developing stable crosslinkers, are likely to become increasingly important research areas in the future.

Aqua/Mechanochemical Mediated Synthesis of Novel Spiro [Indole-Pyrrolidine] Derivatives

Spirocyclic scaffolds are found in many pharmacologically active natural and synthetic compounds. From time to time, efforts have been made to develop new or better processes for the synthesis of spirocyclic compounds. Spiro [Indole-pyrrolidine] Derivatives are readily synthesized in high to excellent yields by the Michael condensation of 3-dicyanomethylene-2H-indol-2-ones (produced via the Knoevenagel condensation of indole-2,3-dione with malononitrile) with isothiocyanate derivatives under aqueous and mechanochemical conditions. The advantages of this protocol are that the reactions are solvent-free, occur at ambient temperature, require short reaction times, have experimental simplicity, and produce excellent yields. These environmentally friendly reaction media are useful alternatives to volatile organic solvents.

Copper Cocatalyst Modulated Radical Generation for Selective Heterogeneous Photosynthesis of α-Haloketones

The α-haloketones are important precursors for synthetic chemistry and pharmaceutical applications; however, their production relies heavily on traditional synthetic methods via halogenation of ketones that are toxic and environmentally risky. Here, we report a heterogeneous photosynthetic strategy of α-haloketone production from aromatic olefins using copper-modified graphitic carbon nitride (Cu-C₃N₄) under mild reaction conditions. By employing NiX₂ (X = Cl, Br) as the halogen source, a series of α-haloketones can be synthesized using atmospheric air as the oxidant under visible-light irradiation. In comparison with pristine carbon nitride, the addition of Cu as a cocatalyst provides a moderate generation rate of halogen radicals and selective reduction of molecular oxygen into ^•OOH radicals, thus leading to a high selectivity to α-haloketones. The Cu-C₃N₄ also exhibits high stability and versatility, rendering it a promising candidate for solar-driven synthetic applications.

ICl-Mediated Functional Group Interconversion from Methyl Homopropargyl Ether to α-Iodo-γ-chloroketone

An ICl-mediated highly chemo- and regioselective functional group interconversion from methyl homopropargyl ether to α-iodo-γ-chloro-ketone is reported. Density functional theory (DFT)-calculated reaction coordinate and potential energy surface support the high chemo-selectivity observed for the formation of α-iodo-γ-chloroketone over furan. The five-membered oxonium ring formation-ring opening mechanism is a potential template for the preparation of polyfunctionalized carbonyl compounds.

Visible-Light-Induced Oxidative α-keto-Dichlorination of Arylalkynes by CuCl2 at Room Temperature

A visible light-induced oxidative α-keto-dichlorination of terminal and internal aryl alkynes was developed to form dichloroacetophenones (DCAPs) and dichlorophenyl-acetophenones (DCPAPs), respectively, by using CuCl₂ as a photoredox catalyst in the presence of air at room temperature (without using any exogenous photocatalyst). Here, photoexcited CuCl₂ underwent ligand-to-metal charge transfer to generate a Cl radical, which readily added to the alkynes to form DCAPs or DCPAPs in the presence of O₂ . This α-keto-dichlorination reaction is a green and mild protocol as it produced water as the only by-product. Moreover, the evaluation of green chemistry metrics indicated that the E-factor (mass of wastes/mass of products) of the current α-keto-chlorination method is around 10.1 times lower than that of a literature-reported photochemical method. The Eco Scale value (score 55, which on a scale of 0-100 indicates an acceptable synthesis) signifies that this process is simple, highly efficient, eco-friendly, and cost-effective.

Synthetic Access to Aromatic α-Haloketones

α-Haloketones play an essential role in the synthesis of complex N-, S-, O-heterocycles; of which some exhibit a remarkable biological activity. Research further illustrated that α-bromo-, α-chloro-, and α-iodoketones are key precursors for blockbuster pharmacological compounds. Over the past twenty years, substantial advances have been made in the synthesis of these industrially relevant building blocks. Efforts have focused on rendering the synthetic protocols greener, more effective and versatile. In this survey, we summarised and thoroughly evaluated the progress of the field, established in the past two decades, in terms of generality, efficacy and sustainability.

Molecular Rearrangement of Pyrazino[2,3-c]quinolin-5(6H)-ones during Their Reaction with Isocyanic Acid

New tetrahydropyrazino[2,3-c]quinolin-5(6H)-ones were prepared from 3-chloroquinoline-2,4(1H,3H)-diones and ethylene diamine. In their reaction with HNCO, an unprecedented molecular rearrangement produced new types of hydantoin derivatives. All prepared compounds were characterized on the basis of their ¹H, ¹³C, and ¹⁵N NMR and ESI mass spectra and some were authenticated by X-ray analysis of single crystalline material. A proposed mechanism for rearrangement is discussed in this essay. The CDK and ABL inhibition activity as well as in vitro cytotoxicity of the prepared compounds was also tested.

Sulfur(iv)-mediated umpolung α-heterofunctionalization of 2-oxazolines

The α-umpolung of carbonyl compounds significantly expands the boundaries of traditional carbonyl chemistry. Despite various umpolung methods available today, reversing the inherent reactivity of carbonyls still remains a substantial challenge. In this article, we report the first use of sulfonium salts, in lieu of well-established hypervalent iodines, for the carbonyl umpolung event. The protocol enables the incorporation of a wide variety of heteroatom nucleophiles into the α-carbon of 2-oxazolines. The success of this investigation hinges on the following factors: (1) the use of sulfoxides, which are abundant, structurally diverse and tunable, and easily accessible, ensures the identification of a superior oxidant namely phenoxathiin sulfoxide for the umpolung reaction; (2) the "assembly/deprotonation" protocol previously developed for rearrangement reactions in our laboratory was successfully applied here for the construction of α-umpoled 2-oxazolines.

Catalytic Oxidations with ortho-Substituted Modified IBXs

IBX is an oxidation reagent that has surged into prominence in the last two decades. It is cost-effective, environmentally benign and readily prepared from o-iodobenzoic acid. However, its insolubility in common organic solvents and explosive attributes upon impact and heating are debilitating disadvantages. Development of modified IBXs,i.e., mIBXs, that exhibit improved solubility and enhanced reactivity, and obviate explosive attributes by a judicious manipulation of the structure of IBX has been an incessant endeavor. In this account, common organic solvent-soluble modified o-iodoxybenzoic acids (mIBXs) developed in our research group are collated with discussion of rationale underlying the design principles. Steric build-up around the iodoxolone moiety that is responsible for strong intermolecular interactions within the crystal lattice of IBX constitutes the key consideration in the design and development of modified λ5-iodanes that are reactive and sparingly soluble in common organic solvents. In situ generation of mIBXs from precursor iodo-acids in the presence of Oxone® permits employment of the latter as organocatalysts for facile oxidative transformations. Reactive mIBXs generated in situ from precursor modified iodoacids (mIAs, I(I)) in the presence of Oxone® may constitute unrivaled prospects for cost-effective oxidations. Applications of mIBXs, generated in situ or otherwise, for efficient oxidations are consolidated.

Selenium Dioxide-Mediated Bromination of α,β-Unsaturated Ketones Using N-Bromosuccinimide in the Presence of p-Toluenesulfonic Acid: A Versatile Route for the Synthesis of α'-Bromo-4-arylbut-3-en-2-one and α',α'-Dibromo-4-arylbut-3-en-2-one

An efficient method for the synthesis of α,β-unsaturated α'-bromoketones and α,β-unsaturated α',α'-dibromoketones is described using N-bromosuccinimide (NBS) as the brominating agent mediated by selenium dioxide (SeO₂) in the presence of p-toluenesulfonic acid (PTSA) monohydrate in toluene. The method is simple, employing easily available shelf reagents to afford a wide range of products in good yields. The method highlighted that simple fine-tuning of the reaction conditions and molar equivalents of the reactants easily affords either mono- or dibrominated products in excellent yields. A number of these products have not been reported in the literature. All of the reactions were carried out in gram-scale quantities.

Acetyl nitrate mediated conversion of methyl ketones to diverse carboxylic acid derivatives

The development of a novel acetyl nitrate mediated oxidative conversion of methyl ketones to carboxylic acid derivatives is described. By analogy to the haloform reaction and supported by experimental and computational investigation we propose a mechanism for this transformation.

Reaction of Tertiary 2-Chloroketones with Cyanide Ions: Application to 3-Chloroquinolinediones

3-Chloroquinoline-2,4-diones react with cyanide ions in dimethyl formamide to give 3-cyanoquinoline-2,4-diones in small yields due to the strong hindrance of the substituent at the C-3 atom. Good yields can be achieved if the substituent at this position is the methyl group. In the methanol solution, the reaction proceeds by an addition mechanism to form 2-oxo-1a,2,3,7b-tetrahydrooxireno[2,3-c]quinoline-7b-carbonitriles, from which 4-hydroxy-3-methoxy-2-oxo-1,2,3,4-tetrahydroquinoline-4-carbonitriles are subsequently formed by opening of the epoxide ring with methanol. Some minor products of these reactions have also been isolated. The 1 H, 13 C and 15 N NMR spectra of the prepared compounds were measured, and all resonances were assigned using appropriate two-dimensional spectra.

Novel N-Arylsulfonylindoles Targeted as Ligands of the 5-HT6 Receptor. Insights on the Influence of C-5 Substitution on Ligand Affinity

A new series of twenty-two C-5 substituted N-arylsulfonylindoles was prepared with the aim of exploring the influence of C-5 substitution on 5-HT₆ receptor affinity. Eleven compounds showed moderate to high affinity at the receptor (K_i = 58–403 nM), with compound 4d being identified as the most potent ligand. However, regarding C-5 substitution, both methoxy and fluorine were detrimental for receptor affinity compared to our previously published unsubstituted compounds. In order to shed light on these observations, we performed docking and molecular dynamics simulations with the most potent compounds of each series (4d and 4l) and PUC-10, a highly active ligand previously reported by our group. The comparison brings about deeper insight about the influence of the C-5 substitution on the binding mode of the ligands, suggesting that these replacements are detrimental to the affinity due to precluding a ligand from reaching deeper inside the binding site. Additionally, CoMFA/CoMSIA studies were performed to systematize the information of the main structural and physicochemical characteristics of the ligands, which are responsible for their biological activity. The CoMFA and CoMSIA models presented high values of q² (0.653; 0.692) and r² (0.879; 0.970), respectively. Although the biological activity of the ligands can be explained in terms of the steric and electronic properties, it depends mainly on the electronic nature.

Synthetic Routes Towards the Synthesis of Geminal α-Difunctionalized Ketones

The importance of gem-difunctionalized ketones is represented by their broad applications across chemical boundaries over recent years. The interesting reactivities that this class of compounds possess have made them ideal building blocks to access high-value organic molecules. Furthermore, the gem-difunctionalized ketone moiety has featured in numerous bioactive molecules. For these reasons, a plethora of routes to access such significant molecules have been developed by research groups worldwide - this account looks at delineating the synthesis of gem-difunctionalized ketones from carbonyl substrates, diazo compounds, sulfur ylides and alkynyl reactants.

1,1,2-Tribromoethyl arenes: novel and highly efficient precursors for the synthesis of 1-bromoalkynes and α-bromoketones

A novel tribromination method to prepare versatile intermediate 1,1,2-tribromoethyl arenes, which can not only be transformed to synthetically valuable 1-bromoalkynes via elimination but also be hydrolyzed to a variety of α-bromoketones, was developed.

Iodine-mediated formal [3 + 2] annulation for synthesis of furocoumarin from oxime esters

A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins. The reaction was proposed to undergo radical mechanism mediated by iodine, a cheap and common laboratory reagent. Mechanistic studies showed the key for the successful transformation was the presence of α-iodoimine intermediate which facilitated the ring-closing step. The developed conditions produced good functional group tolerance with a wide range of high-profile furocoumarin product. The potential for this strategy to be applied in other syntheses of heterocyclic compounds is highly achievable.

A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins.

Fluorohydration of alkynes via I(I)/I(III) catalysis

Substrate specificity is ubiquitous in biological catalysis, but less pervasive in the realm of small-molecule catalysis. Herein, we disclose an intriguing example of substrate specificity that was observed whilst exploring catalysis-based routes to generate α-fluoroketones from terminal and internal alkynes under the auspices of I(I)/I(III) catalysis. Utilising p-TolI as an inexpensive organocatalyst with Selectfluor^® and amine/HF mixtures, the formation of protected α-fluoroketones from simple alkynes was realised. Whilst the transient p-TolIF₂ species generated in situ productively engaged with pentynyl benzoate scaffolds to generate the desired α-fluoroketone motif, augmentation or contraction of the linker suppressed catalysis. The prerequisite for this substructure was established by molecular editing and was complemented with a physical organic investigation of possible determinants.

Dominant formation of unregulated disinfection by-products during electrocoagulation treatment of landfill leachate

During the electrocoagulation (EC) treatment of landfill leachate, the production of chlorine species may result in the formation of harmful disinfection by-products (DBPs). This formation was investigated in the present study by monitoring five classes of DBPs (haloacetic acids-HAA, trihalomethanes-THM, haloacetonitriles-HAN, haloketones-HK, and halonitromethanes-HNM) in two leachate samples treated by EC. It was shown that the applied current has stimulated the formation of DBPs, which were dominated by unregulated DBPs. With a current density of 100 mA cm^-2, the unregulated HK dominated the weight-based DBP concentration (96% in Leachate A and 44.3% in Leachate B), while the unregulated HAN contributed to >80% of the DBP additive toxicity in both leachates. The concentrations of regulated THM and HAA species were below US EPA regulations. The in situ generation of active chlorine has resulted in the DBP formation, as demonstrated in the scavenging test. Applying granular activated carbon as a post-treatment step could successfully reduce the total DBP concentration from 295.33 μg L^-1 to 82.04 μg L^-1 in Leachate A, leading to a total DBP removal of 72.2% and a toxicity removal of 50%. Given the dominant concentration and lack of toxicity information, the unregulated DBPs should receive more attention.