Platinum nanoparticles stabilized by N-heterocyclic thiones. Synthesis and catalytic activity in mono- and di-hydroboration of alkynes.

N-Heterocyclic Thiones (NHT) proved to be efficient ligands for the stabilization of small platinum nanoparticles (1.3-1.7 nm), synthesized by decomposition of [Pt(dba)2], under a H2 atmosphere, in the presence of variable sub-stoichiometric amounts of the NHT. Full characterization by means of TEM, HR-TEM, NMR, ICP, TGA and XPS have been carried out, providing information about the nature of the metal nanoparticles and the interaction of the NHT ligands to the metal surface. Importantly, DFT calculations indicate that some NHT ligands interact with the metal through the C[double bond, length as m-dash]C double bond of the imidazole fragment in addition to the sulfur atom, thus providing additional stabilization to the nanoparticles. According to XPS, TGA and ICP techniques, the surface coverage by the ligand increases by decreasing the size of the substituents on the nitrogen atom. The platinum nanoparticles have been used as catalyst in the hydroboration of alkynes. The most active system is that with a less covered surface area lacking an interaction of the ligand by means of the C[double bond, length as m-dash]C double bond. This catalyst hydroborates alkynes with excellent selectivities towards the monoborylated anti-Markovnikov product (vinyl-boronate) when one equiv. of borane is used. Very interestingly, aliphatic alkynes undergo a second hydroborylation process leading to the corresponding 1,1- and 1,2-diboroylated species with good selectivities towards the former.

Straightforward synthesis of Man9, the relevant epitope of the high-mannose oligosaccharide.

The high-mannose oligosaccharide (or its corresponding Man9 epitope) is the most abundant structure present in pathogen envelope glycoproteins. These glycans play a key role in the pathogenesis of several pathogens and also in the communication with the immune system. Understanding the mechanism of action of these glycans requires the access to pure and chemically well-defined structures in reasonable amounts. The synthesis of these complex branched oligosaccharides is not trivial and few syntheses are reported in the literature with several synthetic and purification steps and low overall yields. In this work, we described a very efficient synthetic alternative to access this relevant Man9 epitope in a very straightforward manner.

Stabilisation of gold nanoparticles by N-heterocyclic thiones.

Gold nanoparticles (Au-NPs) have been prepared using N-heterocyclic thiones (NHTs) as ligand stabilisers. These Au-NPs have been shown to be very stable, even in air, and have been characterized by a combination of several techniques (TEM, HR-TEM, STEM-HAADF, EDX, DLS, elemental analysis and 1H NMR). These nanoparticles are active in the catalytic reduction of nitroarenes to anilines.

Rapid and efficient synthesis of α(1-2)mannobiosides.

α(1,2)mannobiosides with different substituents at the reducing end have been synthesized by a common strategy using benzoyls as the permanent protecting groups and an acetyl as the orthogonal protecting group at position C2 of the glycosyl acceptor. The new synthetic strategy has been performed remarkably reducing the number of purification steps, the time of synthesis (less than 72 hours) and improving the overall yield at least three times with respect to the best procedure described in the literature at the moment. Additionally, this protecting group strategy is compatible with the presence of azido groups and the use of Cu catalyzed azide alkyne cycloaddition (CuAAC) also called "click chemistry" for conjugating the α(1-2)mannobiosides to different scaffolds for the preparation of mannosyl multivalent systems.

Maytenus salicifolia Reissek, Celastraceae: triterpenes isolated from stems and antioxidant property of extracts from aerial parts

Six pentacyclic triterpenes were isolated from hexane extract of stems of Maytenus salicifolia Reissek, Celastraceae: 30-hydroxyfriedelan-3-one (1), 3,16-dioxofriedelane (2), friedeline (3), lupeol (4), betuline (5) and lup-20(29)-en-3,30-diol (6). The structure each one was established on the basis of detailed ¹H and 13C NMR spectral investigation and by comparison with the respective literature values. For compound 1, the complete 2D NMR (HMBC, HMQC and NOESY) spectral data were herein reported for the first time. Compounds 1, 2, 5 and 6 were isolated for the first time from this plant. Antioxidant activity is described for some extracts from species of the Celastraceae family, then, the extracts from aerial parts of M. salicifolia were evaluated in relation to antioxidant potential using the DPPH method. Compared to quecertin, the AcEt extract (EAF) from leaves, AcEt (EAPF) and MeOH (EMPF) from pulp fruit and AcEt (EAT) and MeOH (EMT) from stems showed significant antioxidant property.