Rhodium(II)-Catalyzed Enantioselective Intermolecular Aziridination of Alkenes

C₄-Symmetrical dirhodium(II) tetracarboxylates are highly efficient catalysts for the asymmetric intermolecular aziridination of substituted alkenes with sulfamates. The reaction proceeds with high levels of efficiency and chemoselectivity to afford aziridines with excellent yields of up to 95% and enantiomeric excesses of up to 99%. The scope of the alkene aziridination includes mono-, di-, and trisubstituted olefins as well as the late-stage functionalization of complex substrates. The reaction can be performed on a gram-scale with a catalyst loading of 0.1 mol %. Our DFT study led us to propose a two-spin-state mechanism, involving a triplet Rh-nitrene species as key intermediate to drive the stereocontrolled approach and activation of the substrate.

Synthesis, self-assembly and Langerin recognition studies of a resorcinarene-based glycocluster exposing a hyaluronic acid thiodisaccharide mimetic

Herein, we report the synthesis of an octavalent glycocluster exposing a thiodisaccharide mimetic of the repetitive unit of hyaluronic acid, βSGlcA(1 → 3)βSGlcNAc, constructed on a calix[4]resorcinarene scaffold by CuAAC reaction of suitable precursors. This glycocluster showed a strong tendency toward self-aggregation. DOSY-NMR and DLS experiments demonstrated the formation of spherical micelles of d ≅ 6.2 nm, in good agreement. TEM micrographs showed the presence of particles of different sizes, depending on the pH of the starting solution, thus evidencing that the negative charge on the micelle surface due to ionization of the GlcA residues plays an important role in the aggregation process. STD-NMR and DLS experiments provided evidence of the interaction between the synthetic glycocluster and Langerin, a relevant C-type lectin. This interaction was not observed in the STD-NMR experiments performed with the basic disaccharide, providing evidence of a multivalent effect.

Supramolecular organogels based on mesogenic 2,7-difunctionalized triphenylenes as a simple system for water content assessment in light alcohols

Self-assembly of di-hydroxylated triphenylenes in columnar mesophases and organogels depends on the spacer length and allows water quantification in alcohols.

The effect of vicinal di-halo substituents on the organogelling properties of aromatic supramolecular gelators and their application as soft templates

Vicinal di-halo substituents have a determinant effect on the supramolecular self-assembly and properties of aromatic physical gelators with application as soft templates.

Late-stage C-H amination of abietane diterpenoids

This study aims at highlighting the synthetic versatility of the rhodium-catalyzed C-H amination reactions using iodine(iii) oxidants for the late-stage functionalization of natural products. Inter- and intramolecular nitrene insertions have been performed from various abietane diterpenoids, leading to the amination of the C-3, C-6, C-7, C-11 and C-15 positions. Ca. 20 aminated compounds have been isolated with yields of up to 86% and high levels of regio-, chemo- and stereoselectivities.

Gels as Templates for the Syntheses of Shape-Controlled Nanostructured Materials

The preparation of inorganic, organic and/or hybrid nanostructured materials with controlled shape and size is crucial for the development of nanotechnology, and it is nowadays the focus of intense research.[...].

Synthesis of new C-25 and C-26 steroidal acids as potential ligands of the nuclear receptors DAF-12, LXR and GR

A new methodology to obtain C-25 and C-26 steroidal acids starting from pregnenolone is described. Construction of the side chain was achieved by applying the Mukaiyama aldol reaction with a non-hydrolytic work-up to isolate the trapped silyl enol ether with higher yields. Using this methodology we synthesized three new steroidal acids as potential ligands of DAF-12, Liver X and Glucocorticoid nuclear receptors and studied their activity in reporter gene assays. Our results show that replacement of the 21-CH₃ by a 20-keto group in the side chains of the cholestane scaffold of DAF-12 or Liver X receptors ligands causes the loss of the activity.

Supramolecular Assembly of pH-Sensitive Triphenylene Derived π-Gelators and Their Application as Molecular Template for the Preparation of Silica Nanotubes

The gelation properties and mode of self-assembly of six asymmetrical hexaether triphenylene derivatives mono-functionalized with carboxylic and primary amine groups were investigated. The presence of a carboxylic and amine group attached to the triphenylene core generated stable, thermo- and pH-sensitive supramolecular π-organogels with a reversible response to both stimuli. In order to understand the gelation process, we studied the effect of the spacer length and found a different gelation scope for the acid and basic derivatives that accounts for a different supramolecular self-assembly. The presence of the basic group on the amino derivatives was used to guide and catalyze the templated in situ sol-gel polymerization of TEOS and allowed us, under controlled hydrolytic conditions, to prepare an entangled fibrillar network of silica nanotubes.

Versatile supramolecular organogel with outstanding stability toward aqueous interfaces

In this communication, we report on a novel and versatile low-molecular-weight organogelator. The methanolic gel exhibits an exceptional water-enhanced stability as evidenced by a 30 °C increase in Tg with up to 10%v/v of water. This atypical property not observed with other solvents makes of this supramolecular gel a highly stable matrix compatible with aqueous interfaces. As a proof of principle we present the sensing performance of a symmetric tricarbocyanine fluorophore bearing a Zn(II)chelator unit. The system retained its remarkable physical integrity for a long period of time opening new possibilities for other organic-aqueous interface applications.

Self-assembly of 2,3-dihydroxycholestane steroids into supramolecular organogels as a soft template for the in-situ generation of silicate nanomaterials

Supramolecular gels are an important and interesting class of soft materials that show great potential for many applications. Most of them have been discovered serendipitously, and understanding the supramolecular self-assembly that leads to the formation of the gel superstructure is the key to the directed design of new organogels. We report herein the organogelating property of four stereoisomers of the simple steroid 2,3-dihydroxycholestane. Only the isomer with the trans-diaxial hydroxy groups had the ability to gelate a broad variety of liquids and, thus, to be a super-organogelator for hydrocarbons. The scope of solvent gelation was analysed with regard to two solvent parameters, namely the Kamlet-Taft and the Hansen solubility parameters. The best correlation was observed with the Hansen approach that revealed the existence of two clear gelation zones. We propose a general model of self-assembly through multiple intermolecular hydrogen bonds between the 1,2-dihydroxy system, which is based on experimental data and computational simulations revealing the importance of the di-axial orientation of the hydroxy groups for the one-dimensional self-assembly. Under controlled conditions, the fibrillar superstructure of the organogel was successfully used as a template for the in-situ sol-gel polymerization of tetraethoxysilane and the further preparation of silica nanotubes. We propose that the driving forces for templating are hydrogen bonding and electrostatic interactions between the anionic silicate intermediate species and the self-assembled fibrillar network.

Synthesis of 6-azaprogesterone and 19-hydroxy-6-azasteroids

19-Hydroxy-6-azapregnanes were obtained from pregnenolone via a 7-azido-5-oxo-6-nor-5,7-secopregnane intermediate. The 6-azapregnane core was built in good yield in a straightforward way from the secosteroid, by means of a Staudinger (aza-Wittig) reaction. Finally the 19-hydroxy-6-azapregnane was transformed into 19-hydroxy-6-azaprogesterone (that cyclized spontaneously to the 19→3 hemiketal) and 6-azaprogesterone. The 6-azapregnanes lacked agonistic/antagonistic activity on the progesterone receptor.

Synthesis and GABAA receptor activity of A-homo analogues of neuroactive steroids

A procedure is described for the preparation of A-homo-5-pregnenes via an acid catalyzed rearrangement of cyclopropylcarbinols assisted by microwave irradiation. 3alpha-Hydroxy and 4alpha-hydroxy-A-homo-5-pregnen-20-one, analogues of the neuroactive steroid allopregnanolone, were obtained by means of a regioselective epoxidation of a double bond in the expanded A-ring, using a fructose-derived chiral ketone as catalyst and oxone as oxidant. Although both these compounds were marginally active in inhibiting TBPS binding to GABA(A) receptors, 3beta-hydroxy-A-homo-5-pregnen-20-one was almost as active as allopregnanolone. Reduction of the double bond of the latter compound resulted in a ten fold loss of activity.

Synthesis of 6,19-cyclopregnanes. Constrained analogues of steroid hormones

A procedure for the synthesis of 6,19-cyclopregnanes is described involving an intramolecular alkylation reaction of Delta(4)-3-keto steroids with a 19-mesylate in the presence of KOH in isopropanol. Three 6,19-cyclopregnanes were prepared (4, 5 ,9); in the rat, 6,19-cycloprogesterone (4) and its 21-hydroxy derivative 5 displaced [3H]-dexamethasone from glucocorticoid receptors, the former compound being more active. Both compounds did not compete with [3H]-aldosterone for kidney mineralocorticoid receptors nor with [3H]-R5020 for uterus progesterone receptors.

Sulfonimidamides: Efficient Chiral Iminoiodane Precursors for Diastereoselective Copper-Catalyzed Aziridination of Olefins

N-(p-Toluenesulfonyl)-p-toluenesulfonimidamide reacts with iodosylbenzene to afford in situ a chiral iminoiodane. The latter gives, in the presence of a copper(I) catalyst, a nitrene that is very efficiently transferred under stoichiometric conditions to a variety of alkenes with diastereoselectivities up to 60%. [reaction: see text]