Chemical synthesis of site-selective advanced glycation end products in α-synuclein and its fragments

Advanced glycation end products (AGEs) arise from the Maillard reaction between dicarbonyls and proteins, nucleic acids, or specific lipids. Notably, AGEs are linked to aging and implicated in various disorders, spanning from cancer to neurodegenerative diseases. While dicarbonyls like methylglyoxal preferentially target arginine residues, lysine-derived AGEs, such as N(6)-(1-carboxymethyl)lysine (CML) and N(6)-(1-carboxyethyl)lysine (CEL), are also abundant. Predicting protein glycation in vivo proves challenging due to the intricate nature of glycation reactions. In vitro, glycation is difficult to control, especially in proteins that harbor multiple glycation-prone amino acids. α-Synuclein (aSyn), pivotal in Parkinson's disease and synucleinopathies, has 15 lysine residues and is known to become glycated at multiple lysine sites. To understand the influence of glycation in specific regions of aSyn on its behavior, a strategy for site-specific glycated protein production is imperative. To fulfill this demand, we devised a synthetic route integrating solid-phase peptide synthesis, orthogonal protection of amino acid side-chain functionalities, and reductive amination strategies. This methodology yielded two disease-related N-terminal peptide fragments, each featuring five and six CML and CEL modifications, alongside a full-length aSyn protein containing a site-selective E46CEL modification. Our synthetic approach facilitates the broad introduction of glycation motifs at specific sites, providing a foundation for generating glycated forms of synucleinopathy-related and other disease-relevant proteins.

Transition Metal-Catalyzed Enantioselective Synthesis of Chiral Five- and Six-Membered Benzo O-heterocycles

Enantiomerically enriched five- and six-membered benzo oxygen heterocycles are privileged architectures in functional organic molecules. Over the last several years, many effective methods have been established to access these compounds. However, comprehensive documents cover updated methodologies still in highly demand. In this review, recent transition metal catalyzed transformations lead to chiral five- and six-membered benzo oxygen heterocycles are presented. The mechanism and chirality transfer or control processes are also discussed in details.

Total synthesis of [13 C2 ]-labeled phytosiderophores of the mugineic and avenic acid families

We, herein, report the synthesis of 13 C2 -labeled natural products from the mugineic acid and avenic acid family. These phytosiderophores ("plant iron carriers") are built up from non-proteinogenic amino acids and play a key role in micronutrient uptake in gramineous plants. In this work, two central building blocks are prepared from labeled starting materials (13 C2 -bromoacetic acid, 13 C2 -glycine) and further employed in our recently reported divergent, branched synthetic strategy delivering eight isotopically labeled phytosiderophores. The required labeled building blocks (13 C2 -l-allylglycine and a related hydroxylated derivative) were prepared via enantioselective phase-transfer catalysis and enantio- and diastereoselective aldol condensation with a chiral auxiliary, respectively, both potentially valuable themselves for other synthetic routes toward labeled (natural) products.

Visible-light enabled photochemical reduction of 1,2-dicarbonyl compounds by Hünig's base

A visible-light enabled, chemoselective photoreduction of 1,2-dicarbonyl compounds by using Hünig's base as reductant is reported.

Racemic and enantioselective metal-catalyzed synthesis of SF5-containing diarylmethanols

The racemic and enantioselective metal-catalyzed addition of arylboronic acids to 4- and 3-(pentafluorosulfur)benzaldehydes is reported. The racemic synthesis was accomplished using a Pd-based system and a wide range of arylboronic acids could be used, resulting in yields of 42 to 98% of the corresponding SF₅-containing diarylmethanols. A ruthenium-based system, along with (R,R)-Me-BIPAM as the chiral ligand, was investigated and optimized for the enantioselective version. In this case, while the chiral SF₅-containing diarylmethanols were generally obtained in good yields (up to 94%) and enantioselectivities (up to 98% ee), limitations were also observed. For instance, 4-(pentafluorosulfur)benzaldehyde generally provided slightly better yields than 3-(pentafluorosulfur)benzaldehyde. In addition, lower yields and enantioselectivities were observed when using either 4- and 3-substituted arylboronic acids bearing electron-withdrawing (e.g., CO₂Et, NO₂, CF₃) or 2-substituted arylboronic acids (regardless of the nature of the substituent). Overall, the SF₅-containing diarylmethanols described herein represent novel and potentially useful fluorinated building blocks for the synthesis of biologically active compounds.

Isotope-Labeled Aspartate Sidechain as a Non-Perturbing Infrared Probe: Application to Investigate the Dynamics of a Carboxylate Buried Inside a Protein

Because of their negatively charged carboxylates, aspartate and glutamate are frequently found at the active or binding site of proteins. However, studying a specific carboxylate in proteins that contain multiple aspartates and/or glutamates via infrared spectroscopy is difficult due to spectral overlap. We show, herein, that isotopic-labeling of the aspartate sidechain can overcome this limitation as the resultant ¹³C=O asymmetric stretching vibration resides in a transparent region of the protein IR spectrum. Applicability of this site-specific vibrational probe is demonstrated by using it to assess the dynamics of an aspartate ion buried inside a small protein via two-dimensional infrared spectroscopy.

Rhodium-Catalyzed Enantioselective Arylation of Aliphatic Imines

Chiral rhodium(I)-catalyzed highly enantioselective arylation of aliphatic N-sulfonyl aldimines with arylboronic acids has been developed. This transformation is achieved by the use of a rhodium/bis(phosphoramidite) catalyst to give enantiomerically enriched α-branched amines (up to 99 % ee). In addition, this system enables efficient synthesis of (+)-NPS R-568 and Cinacalcet which are calcimimetic agents.

Cationic Iridium/S-Me-BIPAM-Catalyzed Direct Asymmetric Intermolecular Hydroarylation of Bicycloalkenes

Highly enantioselective cationic iridium-catalyzed hydroarylation of bicycloalkenes, by carbonyl-directed C-H bond cleavage, was accomplished using a newly synthesized sulfur-linked bis(phosphoramidite) ligand (S-Me-BIPAM). The reaction provides alkylated acetophenone or benzamide derivatives in moderate to excellent yields and good to excellent enantioselectivities. Notably, the hydroarylation reaction of 2-norbornene with N,N-dialkylbenzamide proceeds with excellent enantioselectivity (up to 99% ee) and high selectivity for the mono-ortho-alkylation product.

Enantioselective addition of arylboronic acids to methyl 2-formylbenzoates by using a ruthenium/Me-BIPAM catalyst for synthesis of chiral 3-aryl-isobenzofuranones

[RuCl₂(p-cymene)]₂/Me-BIPAM and RuCl₂(PPh₃)₃/Me-BIPAM catalyst systems tolerate a variety of functional groups and give high yields with high enantioselectivities.

Ruthenium/base-catalyzed ortho-selective C–H arylation of acylarenes with halogenated arylboronates

Ruthenium-catalyzed ortho-selective C–H arylation of acylarenes with halogenated arylboronates was promoted by the catalytic amount of bases and provided desired halogenated biaryls in excellent yields under 0.2–1 mol% ruthenium catalyst loading.

Direct asymmetric hydrogenation of α-keto acids by using the highly efficient chiral spiro iridium catalysts

The Ir/SpiroPAP catalyzed direct asymmetric hydrogenation of α-keto acids under mild reaction conditions has been developed.

Enantio- and chemoselective Brønsted-acid/Mg(nBu)2 catalysed reduction of α-keto esters with catecholborane

The first enantio- and chemoselective Brønsted-acid catalysed reduction of α-keto esters with catecholborane has been developed.

Enantioselective synthesis of α-oxy amides via Umpolung amide synthesis

α-Oxy amides are prepared through enantioselective synthesis using a sequence beginning with a Henry addition of bromonitromethane to aldehydes and finishing with Umpolung Amide Synthesis (UmAS). Key to high enantioselection is the finding that ortho-iodo benzoic acid salts of the chiral copper(II) bis(oxazoline) catalyst deliver both diastereomers of the Henry adduct with high enantiomeric excess, homochiral at the oxygen-bearing carbon. Overall, this approach to α-oxy amides provides an innovative complement to alternatives that focus almost entirely on the enantioselective synthesis of α-oxy carboxylic acids.