A straightforward synthesis of functionalized 6H-benzo[c]chromenes from 3-alkenyl chromenes by intermolecular Diels-Alder/aromatization sequence.

A new and metal-free approach to the synthesis of substituted 6H-benzo[c]chromenes has been developed. This three-step synthetic sequence starts from variously substituted salicylaldehydes and α,ß-unsaturated carbonyl compounds to form the chromene core. The de novo ring-forming key step is based on a highly regioselective intermolecular Diels-Alder cycloaddition between 3-vinyl-2H-chromenes and methyl propiolate, followed by oxidative aromatization of the cyclohexadiene cycloadduct intermediate to obtain the final products in good yields (up to 94% over two steps). A modular and divergent design was followed, including a multicomponent reaction, to maximize the scaffold diversity obtained from our approach. The mechanism, investigated by DFT calculations, was confirmed to be concerted through a slightly asynchronous transition state. Energetic analysis of the transition states which have been found confirmed the experimental results in terms of regioselectivity and reactivity tendencies.

2,3-Diaminopropanols Obtained from d-Serine as Intermediates in the Synthesis of Protected 2,3-l-Diaminopropanoic Acid (l-Dap) Methyl Esters.

A synthetic strategy for the preparation of two orthogonally protected methyl esters of the non-proteinogenic amino acid 2,3-l-diaminopropanoic acid (l-Dap) was developed. In these structures, the base-labile protecting group 9-fluorenylmethyloxycarbonyl (Fmoc) was paired to the p-toluensulfonyl (tosyl, Ts) or acid-labile tert-butyloxycarbonyl (Boc) moieties. The synthetic approach to protected l-Dap methyl esters uses appropriately masked 2,3-diaminopropanols, which are obtained via reductive amination of an aldehyde prepared from the commercial amino acid Nα-Fmoc-O-tert-butyl-d-serine, used as the starting material. Reductive amination is carried out with primary amines and sulfonamides, and the process is assisted by the Lewis acid Ti(OiPr)4. The required carboxyl group is installed by oxidizing the alcoholic function of 2,3-diaminopropanols bearing the tosyl or benzyl protecting group on the 3-NH2 site. The procedure can easily be applied using the crude product obtained after each step, minimizing the need for chromatographic purifications. Chirality of the carbon atom of the starting d-serine template is preserved throughout all synthetic steps.

Tumor Targeting by Peptide-Decorated Gold Nanoparticles.

Cancer remains one of the most important challenges in biomedical sciences. Chemotherapeutic agents are very potent molecules that exhibit a significant level of toxicity in numerous tissues of the body, particularly in those characterized by high proliferative activity, such as the bone marrow. The scenario is even more complex in the case of the central nervous system, and in particular brain tumors, where the blood brain barrier limits the efficacy of drug therapies. Integrins, transmembrane proteins widely expressed in different types of cancer (glioblastoma, melanoma, and breast cancer), regulate the angiogenic process and play a pivotal role in tumor growth and invasion. Here, we report a nanotechnology strategy based on the use of AuNPs decorated with an arginine-glycine-aspartic acid-like peptide for the diagnosis and treatment of cancer. Two hours after administration in mice, the accumulation of the peptide-decorated NPs in the subcutaneous tumor was ∼4-fold higher than that of uncoated particles and ∼1.4-fold higher than that of PEGylated particles. Also, in the case of the intracranial tumor model, interesting results were obtained. Indeed, 2 h after administration, the amount of peptide-decorated particles in the brain was 1.5-fold that of undecorated particles and 5-fold that of PEGylated particles. In conclusion, this preliminary study demonstrates the high potential of this carrier developed for diagnostic and therapeutic applications.

General, Mild, and Metal-Free Synthesis of Phenyl Selenoesters from Anhydrides and Their Use in Peptide Synthesis.

A mild, practical, and simple procedure for phenyl selenoesters synthesis from several anhydrides and diphenyl diselenide was developed. This transition-metal-free method provides a straightforward entry to storable Fmoc-amino acid selenoesters which are effective chemoselective acylating reagents. An application to oligopeptide synthesis was illustrated.

Stereoselective Synthesis of Substituted Tetrahydropyrans and Isochromans by Cyclization of Phenylseleno Alcohols.

A selenium-mediated strategy for the stereoselective synthesis of substituted tetrahydropyrans and isochromans has been developed starting from δ-phenylseleno ketones. After enantioselective reduction, the chiral nonracemic phenylseleno alcohols were oxidized to the corresponding selenones, which underwent an effcient 6-exo-tet ring-closure reaction.

Synthesis of D-erythro-sphinganine through serine-derived α-amino epoxides.

A total synthesis of D-erythro-sphinganine [(2S,3R)-2-aminooctadecane-1,3-diol] starting from commercial N-tert-butyloxycarbonyl-L-serine methyl ester is described. The approach is based on the completely stereoselective preparation of an α-amino epoxide obtained by treating a protected L-serinal derivative with dimethylsulfoxonium methylide. The oxirane synthon is obtained with an anti configuration fitting the (2S,3R) stereochemistry of the 2-amino-1,3-diol polar head of D-erythro-sphinganine. The synthetic procedure afforded the target compound in a 68% overall yield based on the initial amount of the starting L-serine material.

Magnesium bis(monoperoxyphthalate) hexahydrate as mild and efficient oxidant for the synthesis of selenones.

A new, efficient and mild method for the direct oxidation of selenides to selenones using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) has been developed. Noteworthy this transformation proceeds at room temperature, employs a cheap and safety oxidant and has a broad functional group tolerance. Moreover, the produced selenones could be useful intermediates for the synthesis of different heterocyclic compounds.

Synthesis of enantiopure sugar-decorated six-armed triptycene derivatives.

A new class of molecules with a triptycene rigid core surrounded by six monosaccharide residues was synthesized. Hexakis(bromomethyl) substituted triptycene was converted into a six-armed triptycene azide (2,3,6,7,14,15-hexakis(azidomethyl)-9,10-dihydro-9,10-[1',2']benzenoanthracene). The key step of the synthesis was the cycloaddition of the azide to 2-propyn-1-yl ß-D-gluco- or galactopyranosides. All products were isolated in good yields and were fully characterized.

High-pressure-promoted Diels-Alder approach to biaryls: application to the synthesis of the cannabinols family.

Diels-Alder reactions of a range of 1-(alkoxy/alkyl/halogen-substituted phenyl)buta-1,3-dienes with methyl propiolate carried out in a green ethanolic medium under 9 kbar pressure were investigated. The use of high pressure as activating method of the Diels-Alder reactions allows efficient and regioselective generation of a series of cyclohexadienyl-benzene cycloadducts that are oxidized to the corresponding biaryls. The alkoxy/alkyl/halogen-substituted biaryls produced are useful precursors for accessing substituted 6H-benzo[c]chromen-6-ones and the cannabinols family.

Chemoselective and metal-free reduction of α,ß-unsaturated ketones by in situ produced benzeneselenol from O-(tert-butyl) Se-phenyl selenocarbonate.

The carbon-carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol. This mild, metal-free and experimentally simple reduction procedure displays considerable functional-group compatibility, products are obtained in good to excellent yields, and the use of toxic Se/CO mixture and NaSeH, or the smelly and air-sensitive benzeneselenol, is avoided.

Stereospecific synthesis of beta3-amino acid derivatives from propargylic alcohols: efficient solution-phase synthesis of oligopeptides without coupling agents.

A stereospecific synthesis of beta(3)-amino acids has been accomplished starting from readily available and enantioenriched propargylic alcohols. This conversion can be effected in only three steps by selenium-mediated organic transformations of the carbon-carbon triple bond. This method is especially attractive because the reactive Se-phenyl selenocarboxylate intermediates can be trapped with the amine functionality of an amino acid derivative. Through this strategy a chain elongation at the N-terminus has been effected. The N-deprotection and repetition of the homologation with other Se-phenyl selenocarboxylate intermediates produced beta- and mixed alpha/beta-oligopeptides without the use of coupling agents.

Sequestering ability to Cu2+ of a new bodipy-based dye and its behavior as in vitro fluorescent sensor.

A Bodipy (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivative has been conceived and synthesized starting from l-aspartic acid, as a selective turn-off sensor of Cu2+ ions. Its acid-base properties were determined to study the formation of metal/sensor complex species by titration of solutions each containing a different metal ion, such as Cu2+, Ca2+, Zn2+, Pb2+ and Hg2+ and different metal/sensor ratios. The speciation models allowed us to simulate the distribution of the metal/sensor complex species at the normal concentrations of the corresponding metals present in biological fluids. The distribution diagrams, obtained by varying the concentration of sensor 1, clearly indicate that sensor 1 responds selectively to Cu2+ at micromolar concentrations, even in the presence of other more abundant metal cations Ca2+. Finally, we analyzed the cellular uptake of sensor 1 on human erythrocytes and its ability to chelate Cu2+ in the cellular environment. Results indicate that it crosses the plasmatic membrane and colors the cells of a bright fluorescent red. Exposing the fluorescent cells to Cu2+ results in a complete cellular photobleaching of the red fluorescence, indicating that sensor 1 is able to detect metal changes in the cytosolic environment.

A chiral electrophilic selenium reagent to promote the kinetic resolution of racemic allylic alcohols.

[reaction: see text] The first example of a kinetic resolution process promoted by electrophilic selenium reagents is reported. Racemic allylic alcohols react with half equivalents of a selenenylating agent in methanol leading to the regiospecific formation of the corresponding addition products with a very high level of facial selectivity (from 95:5 to 98:2 dr). The unreacted alcohols can be recovered in an optically enriched form (from 90 to 94% ee).

Intramolecular Nucleophilic Deselenenylation Reactions Promoted by Benzeneselenenyl Triflate. Stereospecific Synthesis of Vicinal Amino Alcohol Precursors.

After activation with electrophilic selenenylating agents, the phenylseleno group of vicinal azido selenides, containing internal oxygen or nitrogen nucleophilic substituents, readily undergoes intramolecular nucleophilic displacement to afford azido-substituted heterocyclic compounds. This intramolecular substitution occurs with inversion of configuration at the carbon atom bearing the selenium atom. Starting from acetamido selenides and carbamato selenides, a stereocontrolled synthesis of the vicinal amino alcohol precursor oxazolines and oxazolidin-2-ones has been developed.

Intramolecular displacement of phenylselenone by a hydroxy group: stereoselective synthesis of 2-substituted tetrahydrofurans.

An efficient and stereocontrolled synthesis of 2-substituted tetrahydrofurans has been achieved. The approach employs the asymmetric reduction of γ-phenylseleno ketones obtained by three different procedures that are peculiarly applied to the synthesis of such compounds. Finally, the intramolecular substitution of the phenylselenone residue by the oxygen atom of a hydroxy group gives the tetrahydrofuran ring.

Antioxidant Properties of Seeds from Lines of Artichoke, Cultivated Cardoon and Wild Cardoon.

The artichoke (Cynara cardunculus L. subsp. scolymus L.), the cultivated cardoon (Cynara cardunculus var. altilis DC.) and the wild cardoon (Cynara cardunculus var. sylvestris L.) are species widely distributed in the Mediterranean area. The aim of this research was to evaluate the antioxidant properties of seeds from lines of artichoke and cultivated and wild cardoon in both aqueous-organic extracts and their residues by FRAP (Ferric Reducing Antioxidant Power) and TEAC (Trolox Equivalent Antioxidant Capacity) evaluations. Both artichoke and cardoon seeds are a good source of antioxidants. Among artichoke seeds, hydrolysable polyphenols contribution to antioxidant properties ranged from 41% to 78% for FRAP values and from 17% to 37% for TEAC values. No difference between cultivated and wild cardoon in antioxidant properties are reported. Our results could provide information about the potential industrial use and application of artichoke and/or cardoon seeds.

Stereocontrolled synthesis of substituted N-arenesulfonyl azetidines from gamma-(phenylseleno)alkyl arylsulfonamides.

Different synthetic methodologies for the stereocontrolled synthesis of substituted azetidines are reported. The approach utilizes an optimized oxidation reaction of gamma-(phenylseleno)alkyl arylsulfonamides, followed by the intramolecular substitution of the resulting phenylselenonyl group by the nitrogen atom.

Ring-closure reactions through intramolecular displacement of the phenylselenonyl group by nitrogen nucleophiles: a new stereospecific synthesis of N-tosyl and N-benzoyl-1,3-oxazolidin-2-ones from beta-hydroxyalkyl phenyl selenides.

A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available beta-hydroxyalkyl phenyl selenides is presented. After transformation into the N-tosyl or N-benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure beta-hydroxyalkyl phenyl selenides as starting materials.

Preparation of a new chiral non-racemic sulfur-containing diselenide and applications in asymmetric synthesis.

The synthesis of the new chiral non-racemic sulfur-containing diselenide, di-2-methoxy-6-[(1S)-1-(methylthio)ethyl]phenyl diselenide, is described. When treated with ammonium persulfate this diselenide is transformed into the corresponding selenenyl sulfate, which acts as a strong electrophilic reagent and adds to alkenes, in the presence of methanol or water, to afford the products of selenomethoxylation or selenohydroxylation, respectively, with excellent diastereoselectivities. Starting from alkenes containing internal nucleophiles, asymmetric cyclofunctionalization reactions also resulted in good chemical yields, complete regioselectivities, and high diastereoselectivities. This sulfur-containing diselenide can also be used in catalytic amounts to promote one-pot selenenylation-deselenenylation processes, from which several types of products can be obtained in high yield and with good enantiomeric excess.