Asymmetric phosphorylation through catalytic P(III) phosphoramidite transfer: enantioselective synthesis of D-myo-inositol-6-phosphate

Catalytic Approaches to Chemo- and Site-Selective Transformation of Carbohydrates

Carbohydrates are a fundamental unit playing pivotal roles in all the biological processes. It is thus essential to develop methods for synthesizing, functionalizing, and manipulating carbohydrates for further understanding of their functions and the creation of sugar-based functional materials. It is, however, not trivial to develop such methods, since carbohydrates are densely decorated with polar and similarly reactive hydroxy groups in a stereodefined manner. New approaches to chemo- and site-selective transformations of carbohydrates are, therefore, of great significance for revolutionizing sugar chemistry to enable easier access to sugars of interest. This review begins with a brief overview of the innate reactivity of hydroxy groups of carbohydrates. It is followed by discussions about catalytic approaches to enhance, override, or be orthogonal to the innate reactivity for the transformation of carbohydrates. This review avoids making a list of chemo- and site-selective reactions, but rather focuses on summarizing the concept behind each reported transformation. The literature references were sorted into sections based on the underlying ideas of the catalytic approaches, which we hope will help readers have a better sense of the current state of chemistry and develop innovative ideas for the field.

Structural Determination and Chemical Synthesis of the N-Glycan from the Hyperthermophilic Archaeon Thermococcus kodakarensis

Asparagine-linked protein glycosylations (N-glycosylations) are one of the most abundant post-translational modifications and are essential for various biological phenomena. Herein, we describe the isolation, structural determination, and chemical synthesis of the N-glycan from the hyperthermophilic archaeon Thermococcus kodakarensis. The N-glycan from the organism possesses a unique structure including myo-inositol, which has not been found in previously characterized N-glycans. In this structure, myo-inositol is highly glycosylated and linked with a disaccharide unit through a phosphodiester. The straightforward synthesis of this glycan was accomplished through diastereoselective phosphorylation and phosphodiester construction by S_N 2 coupling. Considering the early divergence of hyperthermophilic organisms in evolution, this study can be expected to open the door to approaching the primitive function of glycan modification at the molecular level.

Cu-catalysed enantioselective radical heteroatomic S-O cross-coupling

The transition-metal-catalysed cross-coupling reaction has established itself as one of the most reliable and practical synthetic tools for the efficient construction of carbon-carbon/heteroatom (p-block elements other than carbon) bonds in both racemic and enantioselective manners. In contrast, development of the corresponding heteroatom-heteroatom cross-couplings has so far remained elusive, probably due to the under-investigated and often challenging heteroatom-heteroatom reductive elimination. Here we demonstrate the use of single-electron reductive elimination as a strategy for developing enantioselective S-O coupling under Cu catalysis, based on both experimental and theoretical results. The reaction manifests its synthetic potential by the ready preparation of challenging chiral alcohols featuring congested stereocentres, the expedient valorization of the biomass-derived feedstock glycerol, and the remarkable catalytic 4,6-desymmetrization of inositol. These results demonstrate the potential of enantioselective radical heteroatomic cross-coupling as a general chiral heteroatom-heteroatom formation strategy.

Site-Selective Acylation of Pyranosides with Immobilized Oligopeptide Catalysts in Flow

We report the site-selective acetylation of partially protected monosaccharides using immobilized oligopeptide catalysts, which are readily accessible via solid-phase peptide synthesis. The catalysts are able to invert the intrinsic selectivity, which was determined using N-methylimidazole, for a variety of pyranosides. We demonstrate that the catalysts are stable for multiple reaction cycles and can be easily reused after separation from the reaction solution. The catalysts can also be used in flow without loss of reactivity and selectivity.

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.

Asymmetric Synthesis of Stereogenic Phosphorus P(V) Centers Using Chiral Nucleophilic Catalysis

Organophosphates have been widely used in agrochemistry, as reagents for organic synthesis, and in biochemistry. Phosphate mimics possessing four unique substituents, and thereby a chirality center, are useful in transition metal catalysis and as nucleotide therapeutics. The catalytic, stereocontrolled synthesis of phosphorus-stereogenic centers is challenging and traditionally depends on a resolution or use of stochiometric auxiliaries. Herein, enantioenriched phosphorus centers have been synthesized using chiral nucleophilic catalysis. Racemic H-phosphinate species were coupled with nucleophilic alcohols under halogenating conditions. Chiral phosphonate products were synthesized in acceptable yields (33-95%) and modest enantioselectivity (up to 62% ee) was observed after identification of an appropriate chiral catalyst and optimization of the solvent, base, and temperature. Nucleophilic catalysis has a tremendous potential to produce enantioenriched phosphate mimics that could be used as prodrugs or chemical biology probes.

Catalytic asymmetric and stereodivergent oligonucleotide synthesis

We report the catalytic stereocontrolled synthesis of dinucleotides. We have demonstrated, for the first time to our knowledge, that chiral phosphoric acid (CPA) catalysts control the formation of stereogenic phosphorous centers during phosphoramidite transfer. Unprecedented levels of diastereodivergence have also been demonstrated, enabling access to either phosphite diastereomer. Two different CPA scaffolds have proven to be essential for achieving stereodivergence: peptide-embedded phosphothreonine-derived CPAs, which reinforce and amplify the inherent substrate preference, and C2-symmetric BINOL-derived CPAs, which completely overturn this stereochemical preference. The presently reported catalytic method does not require stoichiometric activators or chiral auxiliaries and enables asymmetric catalysis with readily available phosphoramidites. The method was applied to the stereocontrolled synthesis of diastereomeric dinucleotides as well as cyclic dinucleotides, which are of broad interest in immuno-oncology as agonists of the stimulator of interferon genes (STING) pathway.

Asymmetric Catalysis Mediated by Synthetic Peptides, Version 2.0: Expansion of Scope and Mechanisms

Low molecular weight synthetic peptides have been demonstrated to be effective catalysts for an increasingly wide array of asymmetric transformations. In many cases, these peptide-based catalysts have enabled novel multifunctional substrate activation modes and unprecedented selectivity manifolds. These features, along with their ease of preparation, modular and tunable structures, and often biomimetic attributes make peptides well-suited as chiral catalysts and of broad interest. Many examples of peptide-catalyzed asymmetric reactions have appeared in the literature since the last survey of this broad field in Chemical Reviews (Chem. Rev. 2007, 107, 5759-5812). The overarching goal of this new Review is to provide a comprehensive account of the numerous advances in the field. As a corollary to this goal, we survey the many different types of catalytic reactions, ranging from acylation to C-C bond formation, in which peptides have been successfully employed. In so doing, we devote significant discussion to the structural and mechanistic aspects of these reactions that are perhaps specific to peptide-based catalysts and their interactions with substrates and/or reagents.

Catalytic Chemoselective O-Phosphorylation of Alcohols

Phosphorylation of alcohols is a fundamentally important reaction in both life science and physical science. Product phosphate monoesters play key roles in living organisms, natural products, pharmaceuticals, and organic materials. Most of the chemical methods to date for synthesizing phosphate monoesters, however, require multistep sequences or are limited to specific types of substrates possibly due to harsh conditions. An alternative way to enable the simple production of phosphate monoesters from highly functionalized precursor alcohols is, thus, highly desired. We report herein a catalytic phosphorylation of alcohols with high functional group tolerance using tetrabutylammonium hydrogen sulfate (TBAHS) and phosphoenolpyruvic acid monopotassium salt (PEP-K) as the catalyst and phosphoryl donor, respectively. This method enables the direct introduction of a nonprotected phosphate group to the hydroxy group of a diverse menu of alcohol substrates, including functionalized small molecules, carbohydrates, and unprotected peptides. Nuclear magnetic resonance, mass spectrometric, and density functional theory analyses suggest that an unprecedented mixed anhydride species, generated from PEP-K and TBAHS, acts as an active phosphoryl donor in this reaction. This operationally simple and chemoselective catalytic phosphorylation allows for the efficient production of densely functionalized O-phosphorylated compounds, which are useful in diverse fields including biology and medicine.

Catalytic Sulfamoylation of Alcohols with Activated Aryl Sulfamates

We report a new catalytic method for alcohol sulfamoylation that deploys electron-deficient aryl sulfamates as activated group transfer reagents. The reaction utilizes the simple organic base N-methylimidazole, proceeds under mild conditions, and provides intrinsic selectivity for 1° over 2° alcohols (up to >40:1 for certain nucleosides). The requisite aryl sulfamate donors are stable crystalline solids that can be readily prepared on a large scale. Mechanistic considerations support the intermediacy of HNSO₂ "aza-sulfene" in the transfer reaction.

A Short Historical Perspective of Methods in Inositol Phosphate Research

The multitudinous inositol phosphate family elicits a wide range of molecular effects that regulate countless biological responses. In this review, I provide a methodological viewpoint of the manner in which key advances in the field of inositol phosphate research were made. I also note some of the considerable challenges that still lie ahead.

Yb(OTf)3-Catalyzed Desymmetrization of myo-Inositol 1,3,5-Orthoformate and Its Application in the Synthesis of Chiral Inositol Phosphates

A variety of inositol phosphates including myo-inositol 1,4,5-trisphosphate, which is a secondary messenger in transmembrane signaling, were selectively synthesized via Yb(OTf)₃-catalyzed desymmetrization of myo-inositol 1,3,5-orthoformate using a proline-based chiral anhydride as an acylation precursor. The investigated catalytic system could regioselectively differentiate the enantiotopic hydroxy groups of myo-inositol 1,3,5-orthoformate in the presence of a chiral auxiliary. This key step to generate a suitably protected chiral myo-inositol derivatives is described here as a unified approach to access inositol phosphates.

Regiodivergent Glycosylations of 6-Deoxy-erythronolide B and Oleandomycin-Derived Macrolactones Enabled by Chiral Acid Catalysis

This work describes the first example of using chiral catalysts to control site-selectivity for the glycosylations of complex polyols such as 6-deoxyerythronolide B and oleandomycin-derived macrolactones. The regiodivergent introduction of sugars at the C3, C5, and C11 positions of macrolactones was achieved by selecting appropriate chiral acids as catalysts or through introduction of stoichiometric boronic acid-based additives. BINOL-based chiral phosphoric acids (CPAs) were used to catalyze highly selective glycosylations at the C5 positions of macrolactones (up to 99:1 rr), whereas the use of SPINOL-based CPAs resulted in selectivity switch and glycosylation of the C3 alcohol (up to 91:9 rr). Additionally, the C11 position of macrolactones was selectively functionalized through traceless protection of the C3/C5 diol with boronic acids prior to glycosylation. Investigation of the reaction mechanism for the CPA-controlled glycosylations revealed the involvement of covalently linked anomeric phosphates rather than oxocarbenium ion pairs as the reactive intermediates.

Chiral phosphoric acid-catalyzed desymmetrizative glycosylation of 2-deoxystreptamine and its application to aminoglycoside synthesis

This work describes chiral phosphoric acid (CPA)-catalyzed desymmetrizative glycosylation ofmeso-diol derived from 2-deoxystreptamine.

Regioselective phosphorylation of myo-inositol with BINOL-derived phosphoramidites and its application for protozoan lysophosphatidylinositol

BINOL-derived phosphoramidites enabled a regioselective phosphorylation of myo-inositol. The method was applied for the first total synthesis of a protozoan lysophosphatidylinositol, EhPIa.

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

The chemoselective phosphorylation of hydroxyl containing amino acid derivatives and polyols by phosphoryl chlorides catalyzed by 2-aryl-4-(dimethylamino)pyridine-N-oxides is described.

Exploiting Enzymatic Dynamic Reductive Kinetic Resolution (DYRKR) in Stereocontrolled Synthesis

Over the past two decades, the domains of both frontline synthetic organic chemistry and process chemistry and have seen an increase in crosstalk between asymmetric organic/organometallic approaches and enzymatic approaches to stereocontrolled synthesis. This review highlights the particularly auspicious role for dehydrogenase enzymes in this endeavor, with a focus on dynamic reductive kinetic resolutions (DYRKR) to "deracemize" building blocks, often setting two stereocenters in so doing. The scope and limitations of such dehydrogenase-mediated processes are overviewed, as are future possibilities for the evolution of enzymatic DYRKR.

New paradigms for the chiral synthesis of inositol phosphates

Paradigms found: Inositol phosphates are biomolecules found ubiquitously in eukaryotes, in which they play a number of vital biological roles. Their enantioselective synthesis has recently received a boost from two complementary phosphorylation methods that could change the way they are synthesised, and hopefully provide invaluable chemical biology tools to further our understanding of this large family.

Synthesis of densely phosphorylated bis-1,5-diphospho-myo-inositol tetrakisphosphate and its enantiomer by bidirectional P-anhydride formation

The ubiquitous mammalian signaling molecule bis-diphosphoinositol tetrakisphosphate (1,5-(PP)2 -myo-InsP4 , or InsP8 ) displays the most congested three-dimensional array of phosphate groups found in nature. The high charge density, the accumulation of unstable P-anhydrides and P-esters, the lack of UV absorbance, and low levels of optical rotation constitute severe obstacles to its synthesis, characterization, and purification. Herein, we describe the first procedure for the synthesis of enantiopure 1,5-(PP)2 -myo-InsP4 and 3,5-(PP)2 -myo-InsP4 utilizing a C2 -symmetric P-amidite for desymmetrization and concomitant phosphitylation followed by a one-pot bidirectional P-anhydride-forming reaction that combines sixteen chemical transformations with high efficiency. The configuration of these materials is unambiguously shown by subsequent X-ray analyses of both enantiomers after being individually soaked into crystals of the kinase domain of human diphosphoinositol pentakisphosphate kinase 2.

Desymmetrization of 4,6-diprotected myo-inositol

The asymmetric desymmetrization of 4,6-diprotected myo-inositol derivatives was achieved by using a bifunctional, readily available nucleophilic catalyst. The orthogonally protected products were obtained in 80-99% yield with 90-99% ee. Such structures serve as potential enantiopure building blocks for the synthesis of myo-inositol phosphates.

Alternative synthetic tools to phospho-specific antibodies for phosphoproteome analysis: progress and prospects

Signal transduction cascades in living systems are often controlled via post-translational phosphorylation and dephosphorylation of proteins. These processes are catalyzed in vivo by kinase and phosphatase enzymes, which consequently play an important role in many disease states, including cancer and immune system disorders. Current techniques for studying the phosphoproteome (isotopic labeling, chromatographic techniques, and phosphospecific antibodies), although undoubtedly very powerful, have yet to provide a generic tool for phosphoproteomic analysis despite the widespread utility such a technique would have. The use of small molecule organic catalysts that can promote selective phosphate esterification could provide a useful alternative to current state-of-the-art techniques for use in, e.g., the labeling and pull-down of phosphorylated proteins. This report reviews current techniques used for phosphoproteomic analysis and the recent use of small molecule peptide-based catalysts in phosphorylation reactions, indicating possible future applications for this type of catalyst as synthetic alternatives to phosphospecific antibodies for phosphoproteome analysis.

Electronic tuning of site-selectivity

Site-selective functionalizations of complex small molecules can generate targeted derivatives with exceptional step efficiency, but general strategies for maximizing selectivity in this context are rare. Here, we report that site-selectivity can be tuned by simply modifying the electronic nature of the reagents. A Hammett analysis is consistent with linking this phenomenon to the Hammond postulate: electronic tuning to a more product-like transition state amplifies site-discriminating interactions between a reagent and its substrate. This strategy transformed a minimally site-selective acylation reaction into a highly selective and thus preparatively useful one. Electronic tuning of both an acylpyridinium donor and its carboxylate counterion further promoted site-divergent functionalizations. With these advances, we achieve a range of modifications to just one of the many hydroxyl groups appended to the ion channel-forming natural product amphotericin B. Thus, electronic tuning of reagents represents an effective strategy for discovering and optimizing site-selective functionalization reactions.

Site-selective bromination of vancomycin

We report the site-selective bromination of vancomycin to produce, with substantial efficiency, previously unknown monobromovancomycins, a dibromovancomycin, and a tribromovancomycin. We document the inherent reactivity of native vancomycin toward N-bromophthalimide. We then demonstrate significant rate acceleration and perturbation of the inherent product distribution in the presence of a rationally designed peptide-based promoter. Alternative site selectivity is observed as a function of solvent and replacement of the peptide with guanidine.