Highly efficient and selective phosphorylation of amino acid derivatives and polyols catalysed by 2-aryl-4-(dimethylamino)pyridine-N-oxides--towards kinase-like reactivity

N-Sulfonyl Imidazoliums as the Versatile Coupling Reagents and Sulfonating Reagents in Synthesis of Amides, Esters, Thioesters, Phosphoramides, Phosphoesters, Glycosides, Sulfonamides, and Sulfonates

Here, we report a novel strategy for the first time: bench-stable N-sulfonyl imidazoliums were used as the robust and versatile coupling reagents and sulfonating reagents. Fast reactions of N-sulfonyl imidazoliums with carboxylic acids or phosphodiesters formed carboxylic acid-sulfonic acid mixed anhydrides and phospho-sulfonic acid mixed anhydrides, respectively, and the subsequent treatments of the highly active intermediates with the corresponding nucleophilic partners in the presence of imidazoles at room temperature provided amides, dipeptides, carboxylic esters, carboxylic thioesters (almost without racemization during the formation of amides, dipeptides, esters, thioesters), phosphamides, and phosphoesters in high to excellent yields. This kind of N-sulfonyl imidazolium as the coupling reagent was successfully applied in solid phase synthesis of a polypeptide containing 32 amino acid residues. This strategy was effectively extended to the construction of glycosides, and high steroselectivity and good yields were provided. In addition, reactions of N-sulfonyl imidazoliums with amines or alcohols afforded the corresponding sulfonamides and sulfonates in excellent yields. This study should provide a highly efficient, economical, and practical strategy for construction of diverse molecules.

Catalytic Phosphorylation of Tyrosine via a Radical Arbuzov Reaction

Synthetic protein/peptide modification is a powerful strategy for the development of new therapeutics and tools for chemical biology. Accordingly, the development of a synthetic variant of biological tyrosine phosphorylation, a cornerstone of the post-translational modification landscape, could find widespread application in the study of this fundamental biochemical signal. This work describes the development of a mechanistically novel, redox-neutral, photocatalytic tyrosine phosphorylation reaction via a radical Arbuzov-type mechanism. The reaction proceeds with good tyrosine selectivity in di-, tri-, and oligopeptides under mild conditions near neutral pH, tolerating potentially problematic functionality. As the first photocatalytic tyrosine phosphorylation reaction, this work represents a major advance toward the goal of synthetic tyrosine phosphorylation.

Umpolung Phosphorylation of Tyrosine via 1,2-Phospha-Brook Rearrangement

Phosphorylated tyrosine is a fundamental building block of bioactive peptides and proteins. However, the chemoselective phosphorylation of tyrosine over other nucleophilic amino acid residues in unprotected peptides remains a significant challenge. Here we report an umpolung strategy that converts the C-terminal tyrosine into an electrophilic spirolactone cyclohexadienone motif through hypervalent iodine oxidation, followed by a 1,2-phospha-Brook rearrangement using phosphite diesters as nucleophilic phosphoryl donors. This reaction proceeds chemoselectively at the tyrosine phenol and is applicable to a wide range of peptide substrates containing various nucleophilic amino acid residues, including serine and threonine.

A highly efficient catalytic method for the synthesis of phosphite diesters

In contrast to conventional methods that rely on stoichiometric activation of phosphonylating reagents, we have developed a highly efficient catalytic method for the synthesis of phosphite diesters using a readily available phosphonylation reagent and alcohols with environmentally benign Zn(ii) catalysts. Two alcohols could be introduced consecutively on the P center with release of trifluoroethanol as the sole byproduct, without any additive, under mild conditions. The products could be oxidized smoothly to access phosphate triesters. A range of alcohols, including sterically demanding and highly functionalized alcohols such as carbohydrates and nucleosides, can be applied in this reaction.

Stereoselective synthesis of D-glycero-D-manno-heptose-1β,7-bisphosphate (HBP) from D-mannurono-2,6-lactone

The synthesis of D-glycero-D-manno-heptose-1β,7-bisphosphate (HBP) from D-mannose is described. This synthetic approach is notable for the elongation of the seventh carbon, employing mannurono-2,6-lactone, the substrate-controlled establishment of the C-6 configuration, and the nucleophilic introduction of phosphate at the C-1 position through the utilization of 4,6-O-benzylidene-α-triflate.

Lewis-acid-catalyzed phosphorylation of alcohols

An efficient method has been developed for reacting dialkyl H-phosphonates or diarylphosphine oxides with alcohols for constructing C-P bonds. This reaction was catalyzed by Lewis acid and involved nucleophilic substitution. A series of diphenylphosphonates and diphenylphosphine oxides were obtained, from the phosphorylation of alcohols, with good-to-excellent yields.

Four-layer folding framework: design, GAP synthesis, and aggregation-induced emission

The design and synthesis of a type of [1 + 4 + 2] four-layer framework have been conducted by taking advantage of Suzuki-Miyaura cross-coupling and group-assisted purification (GAP) chemistry. The optimized coupling of double-layer diboronic esters with 1-bromo-naphth-2-yl phosphine oxides resulted in a series of multilayer folding targets, showing a broad scope of substrates and moderate to excellent yields. The final products were purified using group-assisted purification chemistry/technology, achieved simply by washing crude products with 95% EtOH without the use of chromatography and recrystallization. The structures were fully characterized and assigned by performing X-ray crystallographic analysis. UV-vis absorption, photoluminescence (PL), and aggregation-induced emission (AIE) were studied for the resulting multilayer folding products.

Recent developments in the cleavage, functionalization, and conjugation of proteins and peptides at tyrosine residues

Peptide and protein selective modification at tyrosine residues has become an exploding field of research as tyrosine constitutes a robust alternative to lysine and cysteine-targeted traditional peptide/protein modification protocols. This review offers a comprehensive summary of the latest advances in tyrosine-selective cleavage, functionalization, and conjugation of peptides and proteins from the past three years. This updated overview complements the extensive body of work on site-selective modification of peptides and proteins, which holds significant relevance across various disciplines, including chemical, biological, medical, and material sciences.

ArPNO-Catalyzed Acylative Dynamic Kinetic Resolution of 3-Hydroxyphthalides: Access to Enantioenriched Phthalidyl Esters

A chiral 4-aryl-pyridine-N-oxide nucleophilic organocatalyst was used to synthesize chiral phthalidyl ester prodrugs by the acylative dynamic kinetic resolution process. By using the 3,5-dimethylphenyl-derived ArPNO catalyst, the phthalidyl esters were obtained in up to 97% yield with 97% ee at room temperature. Two phthalidyl esters of prodrugs, talosalate and talmetacin, were generated. By control experiments and density functional theory calculations, an acyl transfer mechanism was proposed.

Visible-Light-Initiated Multicomponent Reactions of α-Diazoesters to Access Organophosphorus Compounds

A simple visible-light-initiated strategy has been established for the construction of organophosphorus compounds via aerobic multicomponent reaction of α-diazoesters, cyclic ethers, and P(O)H compounds under air. A number of phosphonates and phosphinates could be efficiently isolated in moderate to good yields without the use of photosensitizers and metal reagents. This multicomponent reaction has advantages of mild condition, simple operation, eco-friendly energy, good functional-group tolerance, and gram-scale synthesis.

Controlling the Site Selectivity in Acylations of Amphiphilic Diols: Directing the Reaction toward the Apolar Domain in a Model Diol and the Midecamycin A1 Macrolide Antibiotic

Seeking to improve the site selectivity of acylation of amphiphilic diols, which is induced by imidazole-based nucleophilic catalysts and directs the reaction toward apolar sites, as we recently reported, we examined a new improved catalytic design and an alteration of the acylating agent. The new catalysts performed slightly better selectivity-wise in the model reaction, compared to the previous set, but notably could be prepared in a much more synthetically economic way. The change of the acylating agent from anhydride to acyl chloride, particularly in combination with the new catalysts, accelerated the reaction and increased the selectivity in favor of the apolar site. The new selectivity-inducing techniques were applied to midecamycin, a natural amphiphilic antibiotic possessing a secondary alcohol moiety in each of its two domains, polar as well as apolar. In the case of the anhydride, a basic dimethylamino group, decorating this substrate, overrides the catalyst's selectivity preference and forces selective acylation of the alcohol in the polar domain with a more than 91:1 ratio of the monoacylated products. To counteract the internal base influence, an acid additive was used or the acylating agent was changed to acyl chloride. The latter adjustment leads, in combination with our best catalyst, to the reversal of the ratio between the products to 1:11.

Unconventional Site Selectivity in Palladium-Catalyzed Cross-Couplings of Dichloroheteroarenes under Ligand-Controlled and Ligand-Free Systems

Halides adjacent to nitrogen are conventionally more reactive in Pd-catalyzed cross-couplings of dihalogenated N-heteroarenes. However, a very sterically hindered N-heterocyclic carbene ligand is shown to promote room-temperature cross-coupling at C4 of 2,4-dichloropyridines with high selectivity (∼10:1). This work represents the first highly selective method with a broad scope for C4-coupling of these substrates where selectivity is clearly under ligand control. Under the optimized conditions, diverse substituted 2,4-dichloropyridines and related compounds undergo cross-coupling to form C4-C_(sp2) and C4-C_(sp3) bonds using organoboron, -zinc, and -magnesium reagents. The synthetic utility of this method is highlighted in multistep syntheses that combine C4-selective cross-coupling with subsequent nucleophilic aromatic substitution reactions. The majority of the products herein (71%) have not been previously reported, emphasizing the ability of this methodology to open up underexplored chemical space. Remarkably, we find that ligand-free "Jeffery" conditions enhance the C4 selectivity of Suzuki coupling by an order of magnitude (>99:1). These ligand-free conditions enable the first C5-selective cross-couplings of 2,5-dichloropyridine and 2,5-dichloropyrimidine.

Identification of a Common Pharmacophore for Binding to MMP2 and RGD Integrin: Towards a Multitarget Approach to Inhibit Cancer Angiogenesis and Metastasis

During tumor angiogenesis different growth factors, cytokines and other molecules interact closely with each other to facilitate tumor cell invasion and metastatic diffusion. The most intensively studied as molecular targets in anti-angiogenic therapies are vascular endothelial growth factor (VEGF) and related receptors, integrin receptors and matrix metalloproteinases (MMPs). Considering the poor efficacy of cancer angiogenesis monotherapies, we reasoned combining the inhibition of αvβ3 and MMP2 as a multitarget approach to deliver a synergistic blockade of tumor cell migration, invasion and metastasis. Accordingly, we identified a common pharmacophore in the binding cavity of MMP2 and αvβ3, demonstrating such approach with the design, synthesis and bioassays of tyrosine-derived peptidomimetics carrying the necessary functional groups to bind to key pharmacophoric elements of MMP2 and αvβ3 RGD integrin.

Mild and Chemoselective Phosphorylation of Alcohols Using a Ψ-Reagent

An operationally simple, scalable, and chemoselective method for the direct phosphorylation of alcohols using a P(V)-approach based on the Ψ-reagent platform is disclosed. The method features a broad substrate scope of utility in both simple and complex settings and provides access to valuable phosphorylated alcohols that would be otherwise difficult to obtain.

Goldilocks Effect of Base Strength on Site Selectivity in Acylation of Amphiphilic Diols

Two series of competitive acylation experiments with a polar and an apolar alcohol substrate, imitating two parts of amphiphilic diols, examined the influence of bases of varying strength on the substrate selectivity. While weakly basic 2,4,6-collidine only mildly accelerates the acylation of the polar substrate without affecting that of the apolar one, the acylation of both substrates is drastically hastened by strongly basic DBU. In both cases there is a notable, though not overwhelming, shift of the substrate selectivity towards the polar substrate, compared to the base-free acylation, which favors that of the apolar one. The extraordinarily strong change in the substrate selectivity in favor of the polar substrate was induced, however, by aliphatic tertiary amine bases, DIPEA and Et3N, of ‘Goldilocks’ moderate base strength, which strongly accelerate the acylation of the polar substrate, while almost not affecting that of the apolar one. These effects of the bases on the substrate selectivity are reflected in the site-selectivity trends observed in the acylation of a model diol amphiphile.

Electrochemical Enabled Cascade Phosphorylation of N-H/O-H/S-H Bonds with P-H Compounds: An Efficient Access to P(O)-X Bonds

An electrochemical three component cascade phosphorylation reaction of various heteroatoms-containing nucleophiles including carbazoles, indoles, phenols, alcohols, and thiols with Ph₂ PH has been established. Electricity is used as the "traceless" oxidant and water and air are utilized as the "green" oxygen source. All kinds of structurally diverse organophosphorus compounds with P(O)-N/P(O)-O/P(O)-S bonds are assembled in moderate to excellent yields (three categories of phosphorylation products, 50 examples, up to 97 % yield). A tentative free radical course is put forward to rationalize the reaction procedure.

Desymmetrization of Diols by Phosphorylation with a Titanium-BINOLate Catalyst

The desymmetrization of ten prochiral diols by phosphoryl transfer with a titanium-BINOLate complex is discussed. The phosphorylation of nine 1,3-propane diols is achieved in yields of 50-98%. Enantiomeric ratios as high as 92:8 are achieved with diols containing a quaternary C-2 center incorporating a protected amine. The chiral ligand, base, solvent, and stoichiometry are evaluated along with a nonlinear effect study to support an active catalyst species that is oligomeric in chiral ligand. The use of pyrophosphates as the phosphorylating agent in the desymmetrization facilitates a user-friendly method for enantioselective phosphorylation with desirable protecting groups (benzyl, o-nitrobenzyl) on the phosphate product.

Rational Design of 2-Substituted DMAP-N-oxides as Acyl Transfer Catalysts: Dynamic Kinetic Resolution of Azlactones

A novel concept that conversion of chiral 2-substituted DMAP into its DMAP-N-oxide could significantly enhance the catalytic activity and still be used as an acyl transfer catalyst is presented. A new type of chiral 2-substituted DMAP-N-oxides, derived from l-prolinamides, has been rationally designed, facilely synthesized, and applied in the dynamic kinetic resolution of azlactones. Using simple MeOH as the nucleophile, various l-amino acid derivatives were produced in high yields (up to 98% yield) and enantioselectivities (up to 96% ee). Furthermore, α-deuterium labeled l-phenylalanine derivative was also obtained. Experiments and DFT calculations revealed that in 2-substituted DMAP-N-oxide, the oxygen atom acted as the nucleophilic site and the N-H bond functioned as the H-bond donor. High enantioselectivity of the reaction was governed by steric factors, and the addition of benzoic acid reduced the activation energy by participating in the construction of a H-bond bridge. The theoretical chemical study indicated that only when attack directions of the chiral catalyst were fully considered could the correct calculation results be obtained. This work paves the way for the utilization of the C2 position of the pyridine ring and the development of chiral 2-substituted DMAP-N-oxides as efficient acyl transfer catalysts.

Recent advances in synthetic and medicinal chemistry of phosphotyrosine and phosphonate-based phosphotyrosine analogues

Phosphotyrosine-containing compounds attract significant attention due to their potential to modulate signalling pathways by binding to phospho-writers, erasers and readers such as SH2 and PTB domain containing proteins. Phosphotyrosine derivatives provide useful chemical tools to study protein phosphorylation/dephosphorylation, and as such represent attractive starting points for the development of binding ligands and chemical probes to study biology, and for inhibitor and degrader drug design. To overcome enzymatic lability of the phosphate group, physiologically stable phosphonate-based phosphotyrosine analogues find utility in a wide range of applications. This review covers advances over the last decade in the design of phosphotyrosine and its phosphonate-based derivatives, highlights the improved and expanded synthetic toolbox, and illustrates applications in medicinal chemistry.

Phosphorylation Organocatalysts Highly Active by Design

The activity of nucleophilic organocatalysts for alcohol/phenol phosphorylation was enhanced through attaching oligoether appendages to a benzyl substituent on imidazole- or aminopyridine-based active units, presumably because of stabilizing n-cation interactions of the ethereal oxygens with the positively charged aza-heterocycle in the catalytic intermediates, and was substantially higher than that of known benchmark catalysts for a range of substrates. Density functional theory calculations and the study of analogues having a lower potential for such stabilizing interactions support our hypothesis.

Zinc-Catalyzed Phosphonylation of Alcohols with Alkyl Phosphites

In the presence of a catalytic amount of either Zn(acac)₂ or bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc(II) (Zn(TMHD)₂), primary, secondary, and tertiary alcohol substituents on a wide range of substrates, including acyclic and cyclic structures, carbohydrates, steroids, and amino acids, reacted with dimethyl phosphite to afford the corresponding H-phosphonate diesters in high to excellent yields.

Synthesis and Biological Evaluation of Tryptamines Found in Hallucinogenic Mushrooms: Norbaeocystin, Baeocystin, Norpsilocin, and Aeruginascin

A general synthetic method was developed to access known tryptamine natural products present in psilocybin-producing mushrooms. In vitro and in vivo experiments were then conducted to inform speculations on the psychoactive properties, or lack thereof, of the natural products. In animal models, psychedelic activity by baeocystin alone was not evident using the mouse head twitch response assay, despite its putative dephosphorylated metabolite, norpsilocin, possessing potent agonist activity at the 5-HT_2A receptor.

Phosphorus-containing amino acids with a P–C bond in the side chain or a P–O, P–S or P–N bond: from synthesis to applications

Strategies for the preparation of phosphorus-containing amino acids and their utility in the organic chemistry, physico-chemistry, agrochemistry, and pharmacology fields are reported.

Enantioselective rearrangement of indolyl carbonates catalyzed by chiral DMAP-N-oxides

Bifunctional chiral DMAP-N-oxides, which utilize the oxygen atom as a nucleophilic site, have been reported for the highly enantioselective rearrangement of indolyl carbonates.

Evaluation of Natural and Synthetic Phosphate Donors for the Improved Enzymatic Synthesis of Phosphate Monoesters

Undesired product hydrolysis along with large amounts of waste in form of inorganic monophosphate by-product are the main obstacles associated with the use of pyrophosphate in the phosphatase-catalyzed synthesis of phosphate monoesters on large scale. In order to overcome both limitations, we screened a broad range of natural and synthetic organic phosphate donors with several enzymes on a broad variety of hydroxyl-compounds. Among them, acetyl phosphate delivered stable product levels and high phospho-transfer efficiency at the lower functional pH-limit, which translated into excellent productivity. The protocol is generally applicable to acid phosphatases and compatible with a range of diverse substrates. Preparative-scale transformations using acetyl phosphate synthesized from cheap starting materials yielded multiple grams of various sugar phosphates with up to 433 g L-1 h-1 space-time yield and 75% reduction of barium phosphate waste.

Lathyroxins A and B, Phytotoxic Monosubstituted Phenols Isolated from Ascochyta lentis var. lathyri, a Fungal Pathogen of Grass Pea ( Lathyrus sativus)

Ascochyta lentis var. lathyri has recently been reported to be the causal agent of Ascochyta blight of grass pea ( Lathyrus sativus), a disease characterized by the appearance of necrotic lesions of leaves and stems. Considering the novelty of the pathogen and the possible involvement of secondary metabolites in symptom appearance, a study was carried out to ascertain the capability of this fungus to produce bioactive metabolites. Some phytotoxic phenols were isolated from the culture filtrates of the fungus. In particular, two new phytotoxic metabolites, named lathyroxins A and B, were characterized by spectroscopic methods as 4-(2-hydroxy-3,3-dimethoxypropyl)phenol and 3-(4-hydroxyphenyl)propane-1,2-diol, respectively, and the R absolute configuration of C-2 of their 2-dimethoxy- and 2,3-diol-propyl side chain was assigned. Moreover, other well-known fungal metabolites, namely, p-hydroxybenzaldehyde, p-methoxyphenol, and tyrosol, were also identified. Lathyroxins A and B showed interesting phytotoxic properties, being able to cause necrosis on leaves and to inhibit seed germination and rootlet elongation. Moreover, both of the new metabolites had no effect against bacteria, arthropods, and nematodes.

Kinetic Resolution of 2-Substituted Indolines by N-Sulfonylation using an Atropisomeric 4-DMAP-N-oxide Organocatalyst

The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6-19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.

Crystal structure of 1-methylimidazole 3-oxide monohydrate

1-Methylimidazole 3-N-oxide (NMI-O) crystallizes as a monohydrate, C4H6N2O·H2O, in the monoclinic space group P21 with Z' = 2 (mol-ecules A and B). The imidazole rings display a planar geometry (r.m.s. deviations = 0.0008 and 0.0002 Å) and are linked in the crystal structure into infinite zigzag strands of ⋯NMI-O(A)⋯OH2⋯NMI-O(B)⋯OH2⋯ units by O-H⋯O hydrogen bonds. These chains propagate along the b-axis direction of the unit cell.