Metal-free oxidative lactonization of carbohydrates using molecular iodine

Redox-Neutral Multicatalytic Cerium Photoredox-Enabled Cleavage of O-H Bearing Substrates

The need for synthetic methodologies capable of rapidly altering molecular structure are in high demand. Most existing methods to modify scaffolds rely on net exothermicity to drive the desired transformation. We sought to develop a general strategy for the cleavage of C-C bonds β to hydroxyl groups independent of inherent substrate strain. To this end we have applied a multicatalytic cerium photoredox-based system capable of activating O-H bonds in lactols to deliver formate esters. The same system is also capable of effecting hydrodecarboxylation and hydrodecarbonylation reactions. Initial mechanistic probes demonstrate atomic chlorine (Cl⋅) is generated under the reaction conditions, but substrate activation through cerium-alkoxides or -carboxylates cannot be ruled out.

Industrial-Scale Preparation of a Key Intermediate for the Manufacture of Therapeutic SGLT2 Inhibitors

(3R,4S,5R,6R)-3,4,5-tris(benzyloxy)-6-methyltetrahydro-2H-pyran-2-one (1) is a key intermediate for the preparation of promising SGLT2 inhibitors currently undergoing clinical tests for diabetes therapy. However, fewer reports have demonstrated the preparation of compound 1 at an industrial scale. In this article, an efficient preparation of the intermediate for the industrial production was explored from commercially available methyl-α-D-glucopyranoside in seven steps, including TBS protection, benzyl protection, TBS removal, iodination, reduction, demethylation, and oxidation. The batch of the validation process was 42.82 kg with a HPLC purity of 99.31%. The main advantages of this approach are that the total cost is lower than the reported laboratory-scale synthetic method, the quality is reproducible, and the process is safe and environmentally friendly.

Metal-free hydroxy and aminocyanation of furanos-3-uloses

TSAO-T and ATSAO-T analogues are molecules of interest that are able to inhibit the reverse transcriptase (RT) of HIV-1 and HCV. We also recently highlighted their antiproliferative properties. In all cases, the spiro cycle was a required group for biological activities, which led chemists to produce many derivatives, especially on this ring. These structures can be accessed through the formation of glycoaminonitriles and glycocyanhydrins using methodologies not always adapted to the synthesis of large quantities. Moreover, these latter are poorly versatile (substrate-dependent), need expensive cyanogenic agents and implies the use of a metal in non-catalytic amounts. For this reason, we report here a new metal-free methodology for the synthesis of glycoaminonitriles and glycocyanhydrins using molecular iodine (I₂).

Revisiting applications of molecular iodine in organic synthesis

Molecular iodine contributes significantly to organic transformations in synthetic organic chemistry. It works effectively due to its mild Lewis acidic character, ability as an oxidizing agent, good moisture stability, and easy availability.

Synthetic Route to Glycosyl β-1C-(phosphino)-phosphonates as Unprecedented Stable Glycosyl Diphosphate Analogs and Their Preliminary Biological Evaluation

The synthesis of glycosyl-β-1C-(phosphino)-phosphonates is a challenge since it has not yet been described. In this paper, we report an innovative synthetic method for their preparation from Glc-, Man-, and GlcNAc- lactone derivatives. The proposed original strategy involves the addition of the corresponding δ-hexonolactones onto the dianion of (methylphosphino) phosphonate as a key step, followed by dehydration and stereoselective addition of dihydrogen on the resulting double bond. Final deprotection provides the new glycosyl diphosphate analogs in 35%, 36%, and 10% yield over 6 steps from the corresponding δ-hexonolactones. The synthetized compounds were evaluated as inhibitors of phosphatase and diphosphatase activities and found to have complex concentration-dependent activatory and inhibitory properties on alkaline phosphatase. The synthetized tools should be useful to study other enzymes such as transferases.

Thermal, Spectroscopic, and Crystallographic Analysis of Mannose-Derived Linear Polyols

The major diastereomer formed in the Barbier-type metal-mediated allylation of d-mannose has previously been shown to adopt a perfectly linear conformation, both in solid state and in solution, resulting in the formation of hydrogen-bonded networks and subsequent aggregation from aqueous solution upon stirring. Here, a comprehensive study of the solid state structure of both the allylated d-mannose and its racemic form has been conducted. The binary melting point diagram of the system was determined by differential scanning calorimetry analysis, and the obtained results, along with structure determination by single crystal X-ray diffraction, confirmed that allylated mannose forms a true racemate. Further examination by powder X-ray diffraction and CP MAS ¹³C NMR spectroscopy revealed polymorphism both in the pure enantiomer and in the racemate. In addition, the propargylated and hydrogenated analogues of allylated d-mannose were prepared and subjected to thermal and spectroscopic analyses. The crystal structure of the propargylated compound was successfully determined, showing a linear molecular conformation similar to that found for allylated d-mannose. Both new compounds likewise display aggregation behavior in water, further verifying that the low-energy linear conformation plays a significant role in this unusual behavior of these rodlike mannose derivatives.

Identification of a fluorometabolite from Streptomyces sp. MA37: (2R3S4S)-5-fluoro-2,3,4-trihydroxypentanoic acid

(2R3S4S)-5-Fluoro-2,3,4-trihydroxypentanoic acid (5-FHPA) has been discovered as a new fluorometabolite in the soil bacterium Streptomyces sp. MA37. Exogenous addition of 5-fluoro-5-deoxy-d-ribose (5-FDR) into the cell free extract of MA37 demonstrated that 5-FDR was an intermediate to a range of unidentified fluorometabolites, distinct from fluoroacetate (FAc) and 4-fluorothreonine (4-FT). Bioinformatics analysis allowed identification of a gene cluster (fdr), encoding a pathway to the biosynthesis of 5-FHPA. Over-expression and in vitro assay of FdrC indicated that FdrC is a NAD+ dependent dehydrogenase responsible for oxidation of 5-FDR into 5-fluoro-5-deoxy-lactone, followed by hydrolysis to 5-FHPA. The identity of 5-FHPA in the fermentation broth was confirmed by synthesis of a reference compound and then co-correlation by 19F-NMR and GC-MS analysis. The occurrence of 5-FHPA proves the existence of a new fluorometabolite pathway.

Molecular iodine induced/1,3-dipolar cycloaddition/oxidative aromatization sequence: an efficient strategy to construct 2-substituted benzo[f]isoindole-1,3-dicarboxylates

A useful method for a molecular iodine induced 1,3-dipolar cycloaddition/oxidative aromatization sequence to construct 2-substituted-benzo[f]isoindole-1,3-dicarboxylates is reported.