Iodonium salts are key intermediates in Pd-catalyzed acetoxylation of pyrroles

A mild, room-temperature Pd-catalyzed acetoxylation of pyrroles with phenyliodonium acetate is described. The acetoxylation was found to proceed via the initial formation of pyrrolyl(phenyl)iodonium acetates, which were converted to acetoxypyrroles in the presence of Pd(OAc)(2). The acetoxylation could also be carried out as a one-pot sequential procedure without the isolation of the intermediate iodonium salts.     

Multicomponent pharmaceutical cocrystals: furosemide and pentoxifylline

The combination of the active pharmaceutical ingredients furosemide [4‐chloro‐2‐(furan‐2‐ylmethylamino)‐5‐sulfamoylbenzoic acid] and pentoxifylline [3,7‐dimethyl‐1‐(5‐oxohexyl)‐3,7‐dihydro‐1H‐purine‐2,6‐dione] produces a 1:1 cocrystal, C₁₂H₁₁ClN₂O₅S·C₁₃H₁₈N₄O₃, (I), a 1:1 cocrystal hydrate, C₁₂H₁₁ClN₂O₅S·C₁₃H₁₈N₄O₃·H₂O, (II), and a 1:1 cocrystal acetone solvate, C₁₂H₁₁ClN₂O₅S·C₁₃H₁₈N₄O₃·C₂H₆O, (III). These structures exhibit the presence of a rarely encountered synthon with the graph set R₂²(7). All potential hydrogen‐bond donors of furosemide participate in hydrogen‐bond formation in (I)–(III). However, only two hydrogen‐bond acceptors of furosemide are active in (I) and (II), and only one is active in (III). Four hydrogen‐bond acceptors of pentoxifylline are active in (II), three in (I) and two in (III). These observations are in good agreement with the calculated packing indexes of 69.5, 69.6 and 68.8% for (II), (I) and (III), respectively.     

Weakly-exceptional quotient singularities

A singularity is said to be weakly-exceptional if it has a unique purely log terminal blow-up. In dimension 2, V. Shokurov proved that weakly-exceptional quotient singularities are exactly those of types D _n , E ₆, E ₇, E ₈. This paper classifies the weakly-exceptional quotient singularities in dimensions 3 and 4.     

Synthesis and Applications of Silyl 2‐Methylprop‐2‐ene‐1‐sulfinates in Preparative Silylation and GC‐Derivatization Reactions of Polyols and Carbohydrates

Trimethylsilyl, triethylsilyl, tert‐butyldimethylsilyl, and triisopropylsilyl 2‐methylprop‐2‐ene‐1‐sulfinates were prepared through (CuOTf)₂?C₆H₆‐catalyzed sila‐ene reactions of the corresponding methallylsilanes with SO₂ at 50 °C. Sterically hindered, epimerizable, and base‐sensitive alcohols gave the corresponding silyl ethers in high yields and purities at room temperature and under neutral conditions. As the byproducts of the silylation reaction (SO₂+isobutylene) are volatile, the workup was simplified to solvent evaporation. The developed method can be employed for the chemo‐ and regioselective semiprotection of polyols and glycosides and for the silylation of unstable aldols. The high reactivity of the developed reagents is shown by the synthesis of sterically hindered per‐O‐tert‐butyldimethylsilyl‐α‐d ‐glucopyranose, the X‐ray crystallographic analysis of which is the first for a per‐O‐silylated hexopyranose. The per‐O‐silylation of polyols, hydroxy carboxylic acids, and carbohydrates with trimethylsilyl 2‐methylprop‐2‐ene‐1‐sulfinate was coupled with the GC analysis of nonvolatile polyhydroxy compounds both qualitatively and quantitatively.     

Synthesis and Evaluation of Novel 5-O-(4-C-Aminoalkyl-β-D-ribofuranosyl) Apramycin Derivatives for the Inhibition of Gram-Negative Pathogens Carrying the Aminoglycoside Phosphotransferase(3′)-Ia Resistance Determinant

We report the synthesis and evaluation of two new apramycin 5-O-β-d -ribofuranosides, or apralogs, carrying aminoalkyl branches at the ribofuranose 4-position. This novel modification conveys excellent activity for the inhibition of protein synthesis by wild-type bacterial ribosomes and correspondingly high antibacterial activity against several Gram-negative pathogens. Notably, these new modifications overcome the reduction of antibacterial activity in other 2-deoxystreptamine-type aminoglycosides carrying a 5-O-ribofuranosyl moiety when challenged by the presence of an aminoglycoside phosphotransferase enzyme capable of acting on the ribose 5-position.