Sequential norrish type ii photoelimination and intramolecular aldol cyclization of 1,2-diketones in carbohydrate systems: stereoselective synthesis of cyclopentitols

Opened and closed: Visible-light photostimulation of 2,3-diuloses I triggers an unprecedented sequential rearrangement: A Norrish type II photoelimination to give an isolable acyclic photoenol intermediate II is followed by an intramolecular enolexo aldolization. The contraction of the pyranose ring in this process leads to a new type of cyclopentitol derivative III. R=acyl, alkyl, silyl group

Photochemistry of α-Diketones in carbohydrates : anomalous Norrish typeII photoelimination and Norrish-Yang photocyclization promoted the internal carbonyl group

A series of four α-diketones placed as 1α-pyruvoyl tethers on D-glucopyranose and D-glucopyranosiduronic acid skeletons was prepared in order to determine the influence of captodative and stereoelectronic effects on the regioselectivity of the hydrogen atom transfer (HAT) in Norrish typeII photochemical processes. We observed that the 1,5-HAT regioselectivity can be switched between the two potentially abstractable syn-1,3-diaxial hydrogens at H6 and H8. Highly unusual photoproducts from Norrish typeII photoelimination and Norrish-Yang photocyclization initiated by the excited internal carbonyl group were obtained, in some cases in excellent synthetic yield. The 1,5-HAT transition state in the Norrish typeII photoelimination was investigated by photochemical experiments in the crystalline state

Second generation of thiazolylmannosides, FimH antagonists for E. coli-induced Crohn's disease

International audienceThe anti-adhesive strategy, consisting of disrupting bacterial attachment to the host cells, is widely explored as an alternative to antibiotic therapies. Recently, thiazolylmannosides (TazMans) have been identified as strong anti-adhesives of E. coli strains implied in the gut inflammation of patients with Crohn's disease. In this work, we developed a second generation of TazMans with improved chemical stability. The anomeric nitrogen was substituted by short linkers and the compounds were assessed against the bacterial adhesin FimH and the clinically isolated LF82 E. coli strain in four in vitro assays. The results obtained on the FimH adhesin alone and the whole bacteria enabled the identification of a candidate for further in vivo evaluations

Unsaturated Rh(I) and Rh(III) Naphthyl-based PCP complexes. Major steric effect on reactivity

The addition of an equimolar amount of hydrochloric acid (4.0 M in dioxane) to THF solutions of the binuclear Rh(I) complex [(C10H5(CH2PiPr2)2)Rh(η1-N2)]2 (1a) at room temperature led to an inseparable mixture of 1a, [(C10H5(CH2PiPr2)2)Rh(Cl)(H)] (2a), and [(C10H5(CH2PiPr2)2)Rh(Cl)2 (dioxane)]2 (3a). Exclusive formation of 2a was achieved by slow addition of an equimolar amount of hydrochloric acid (0.4 M in dioxane) to a THF solution of 1a at −35 °C, whereas exclusive formation of 3a was obtained when a second equivalent or an excess (10 equiv) of hydrochloric acid (4.0 M in dioxane) was added to THF solutions of 2a (or to reaction mixtures, which consist of 1a, 2a, and 3a). 3a was structurally characterized. In striking difference to the reactivity pattern of 1a, treatment of THF solutions of the bulky tBu derivative 1b with an equimolar amount or even a large excess (25 equiv) of hydrochloric acid (4.0 M in dioxane) exclusively yielded the hydrido chloro complex [(C10H5(CH2PtBu2)2)Rh(Cl)(H)] (2b). Chloride abstraction from 2a and 2b with AgBF4 exclusively yielded the hydrido rhodium(III) complexes [(C10H5(CH2PR2)2)Rh(H)(F−BF3)] (9a and 9b) with coordination of the counteranion. On the other hand, when an equimolar amount of AgBArF4 was added to methylene chloride (or diethyl ether) solutions of 2a and 2b the cationic, the solvent-stabilized rhodium hydride complexes of type [(C10H5(CH2PR2)2)Rh(solv)(H)][BArF4] (10a and 10b) were formed. If the electron density of the metal centers of 9 (and 10) is reduced further by substitution of the coordinated anion of 9 (or the solvent molecule of 10) with a carbonyl ligand, instant migration of the hydride ligand to the aromatic unit to yield the stable carbonyl complexes of type [(C10H5(CH2PR2)2(H)Rh(CO)][X] (X = BArF4 11a,11b; X = BF4 11a′,11b′) with η2 Caryl−H agostic interactions was observed. Treatment of 2b with CO gas yielded both isomeric forms of [(C10H5(CH2PtBu2)2)Rh(H)(Cl)(CO)] 14b (CO trans to the hydride ligand) and 14b′ (CO trans to the aromatic pincer core). In contrast, when an excess of CO gas was added to THF (or methylene chloride), solutions of 2a, 14a′ was exclusively formed within 20 min at room temperature