Alicia Boto

Catalytic, One-Pot Synthesis of β-Amino Acids from α-Amino Acids. Preparation of (α,β-Peptide Derivatives

The one-pot conversion of readily available alpha-amino acid into beta-amino acid derivatives was carried out in good yields. The method is a sequential process initiated by a tandem radical decarboxylation-oxidation reaction; the resulting acyliminium ion was trapped by silyl ketenes. Stoichiometric and catalytic versions of this reaction were developed and then applied to prepare modified di- and tripeptides. Interestingly, some tripeptides formed expanded beta-turns in the solid state.

Synthesis of alkaloids from amino acids via N-acyliminium ions generated by one-pot radical decarboxylation–oxidation

Abstract A one-pot methodology for the synthesis of α-substituted nitrogen heterocycles from commercial amino acids has been developed. Good stereoselectivity can be achieved with chiral substituted rings. This procedure has been applied to the synthesis of piperidine, pyrrolidine and indolizidinone alkaloids.

One-pot stereoselective synthesis of 1,2-amino alcohol derivatives.

Common β-hydroxy amino acids (such as threonine) can be readily transformed into 1,2-amino alcohols with excellent stereoselectivity. This one-pot decarboxylation-alkylation process allows the replacement of the carboxyl group by alkyl, allyl, or aryl groups, generally in high yields. A variation of the process (decarboxylation-Diels-Alder) allows the formation of bi- and polycyclic systems, which are useful precursors of alkaloid cores or iminosugars.

One-pot synthesis of aryl glycines and other unnatural amino acids from serine derivatives

A mild and highly efficient one-pot synthesis of aryl glycines from easily available serine derivatives is described. This methodology is also applied to the synthesis of other uncommon amino acids.

Tandem oxidative radical decarboxylation-β-iodination of amino acids. Application to the synthesis of chiral 2,3-disubstituted pyrrolidines

Abstract A mild and efficient procedure for the tandem decarboxylation-halogenation of α-amino acids is reported. The iodine is introduced at previously unfunctionalized positions, in good yields. The methodology has been used for the diastereoselective synthesis of 2,3-disubstituted pyrrolidines.

Fragmentation of alkoxy radicals : tandem β-fragmentation-cycloperoxyiodination reaction

Abstract A new tandem β-fragmentation-cycloperoxyiodination reaction is observed when a homoallylic alcohol is irradiated with visible light in the presence of (diacetoxyiodo)benzene and iodine under an atmosphere of oxygen. A synthetically interesting epidioxyiodide medium-sized ketone is obtained by this method.

Conformation and Chiral Effects in α,β,α-Tripeptides

Short α,β,α-tripeptides comprising a central chiral trisubstituted β(2,2,3)*-amino acid residue form unusual γ-turns and δ-turns in CDCl(3) and DMSO-d(6) solutions but do not form β-turns. Thermal coefficients of backbone amide protons, 2D-NMR spectra, and molecular modeling revealed that these motifs were strongly dependent on the configuration (chiral effect) of the central β-amino acid residue within the triad. Accordingly, SSS tripeptides adopted an intraresidual γ-turn like (C6) arrangement in the central β-amino acid, whereas SRS diastereomers preferred an extended δ-turn (C9) conformation. A different SRS-stabilizing bias was observed in the crystal structures of the same compounds, which shared the extended δ-turn (C9) found in solution, but incorporated an additional extended β-turn (C11) to form an overlapped double turn motif.

Sequential alkoxy radical fragmentation-cyclopropylcarbinyl rearrangement. Synthesis of highly functionalized eleven-membered rings

The steroidal 5α-alcohol (3) with (diacetoxyiodo)-benzene and iodine under irradiation with visible light undergoes a tandem alkoxy radical β-fragmentation-cyclopropylcarbinyl rearrangement reaction to give the eleven-membered cyclic ketone (4). Under oxygen pressure peroxidation of the C-radical intermediate takes place to afford the highly functionalized eleven-membered cyclic ketone (6) in moderate yield.

Random laser in biological tissues impregnated with a fluorescent anticancer drug

We have demonstrated that chemically modified anticancer drugs can provide random laser (RL) when infiltrated in a biological tissue. A fluorescent biomarker has been covalently bound to tamoxifen, which is one of the most frequently used drugs for breast cancer therapy. The light emitted by the drug-dye composite is scattered in tissue, which acts as a gain medium. Both non-coherent and coherent RL regimes have been observed. Moreover, the analysis of power Fourier transforms of coherent RL spectra indicates that the tissues show a dominant random laser cavity length of about 18 µm, similar to the average size of single cells. These results show that RL could be obtained from other drugs, if properly marked with a fluorescent tag, which could be appealing for new forms of combined opto-chemical therapies.

Customizable units in di- and tripeptides: selective conversion into substituted dehydroamino acids.

The selective conversion of serine or threonine units of di- and tripeptides into substituted dehydroamino acids is reported. Thus, these common α-amino acids undergo a scission-phosphorylation process to give α-amino phosphonate residues. A Horner-Wadsworth-Emmons reaction with aldehydes or ketones follows to afford the final products with excellent Z-stereoselectivity (Z:E > 98:2). In this way, a single peptide precursor can selectively be transformed into a variety of derivatives.