RESUMEN
Kasugamycin (KSM), an aminoglycoside antibiotic, is composed of three chemical moieties: D-chiro-inositol, kasugamine and glycine imine. Despite being discovered more than 50 years ago, the biosynthetic pathway of KSM remains an unresolved puzzle. Here we report a structural and functional analysis for an epimerase, KasQ, that primes KSM biosynthesis rather than the previously proposed KasF/H, which instead acts as an acetyltransferase, inactivating KSM. Our biochemical and biophysical analysis determined that KasQ converts UDP-GlcNAc to UDP-ManNAc as the initial step in the biosynthetic pathway. The isotope-feeding study further confirmed that 13C, 15N-glucosamine/UDP-GlcNH2 rather than glucose/UDP-Glc serves as the direct precursor for the formation of KSM. Both KasF and KasH were proposed, respectively, converting UDP-GlcNH2 and KSM to UDP-GlcNAc and 2-N'-acetyl KSM. Experimentally, KasF is unable to do so; both KasF and KasH are instead KSM-modifying enzymes, while the latter is more specific and reactive than the former in terms of the extent of resistance. The information gained here lays the foundation for mapping out the complete KSM biosynthetic pathway.
RESUMEN
An example of proaromatic C(alkenyl)-H olefination is reported. This protocol utilized a free carboxylic acid as a directing group for C(alkenyl)-H activation of 1,4-cyclohexadiene and coupled with various alkenes. Direct and sequential bisolefinations of proaromatic acids were achieved. The synthetic applicability has been exhibited by [4 + 2] cycloaddition and decarboxylative aromatization of the resulting proaromatic 1,3-dienes. Additionally, several kinetic studies also have been carried out to elucidate the reaction mechanism.
RESUMEN
In this study, a general procedure was proposed for synthesizing thioethers and selenide ethers from anilines under solvent-free and transition-metal-free conditions. Thioethers were formed when anilines reacted with thiols under blue light-emitting-diode (LED) irradiation at room temperature without a photocatalyst. When reactions were performed using anilines and diselenides, the corresponding selenide ethers were obtained with satisfactory to excellent yields. The reaction was performed under photocatalyst-free and solvent-free conditions without blue LEDs. The advantages of this system include convenient operations, mild reaction conditions, satisfactory functional group tolerance, and late-stage selenylation of drug molecules.
RESUMEN
A palladium-catalyzed synthesis of 2,3-diaryl- N-methylindoles from o-alkynylanilines and aryl pinacol boronic esters was developed. The system possesses high functional group tolerance and a broad substrate scope with a variety of aryl pinacol boronic esters to provide valuable 2,3-diaryl- N-methylindoles in moderate to good yields. Remarkably, the sequential reaction controlled by iridium-catalyzed C-H borylation or palladium-catalyzed alkynylation followed by the present palladium-catalyzed C3 arylation reaction provided functionalized 2,3-diaryl- N-methylindoles in good yields.
RESUMEN
Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.
RESUMEN
An iodine-mediated preparation of ortho-quinone methides (o-QMs) from ortho-hydroxybenzyl alcohols by a C-O bond scission strategy is described. The in situ generated o-QMs were then employed for C-S bond formation by thio-Michael addition of thiols to provide the ortho-hydroxybenzyl thioethers (o-HBT) in moderate to excellent yields.
RESUMEN
A simple and an efficient one-pot three-component reaction of arylamines, aromatic aldehydes, and cyclic ketones was described for the synthesis of various fused quinoline, benzoquinoline, and naphthoquinoline derivatives by using camphorsulfonic acid as a catalyst. The exploitation of pregnenolone steroid for benzoquinolines and terephthalaldehyde for bis-benzoquinolines synthesis was achieved with 68-75% yields. The reactivity of arylamines and the mechanistic study for the formation of benzoquinoline was described precisely. The present protocol offers a great potential for atom-economy under mild conditions.
