Anna Grandas

Diketopiperazine formation in solid phase peptide synthesis using p-alkoxybenzyl ester resins and Fmoc-amino acids

Summary Diketopiperazine formation rates under the usual conditions of a solid phase peptide synthesis cycle with Fmoc-amino acids have been studied on a p -alkoxybenzyl ester resin. Piperidine has been found to be an extremely efficient catalyst for the intramolecular aminolysis reaction.

Mammalian frataxin directly enhances sulfur transfer of NFS1 persulfide to both ISCU and free thiols

Friedreichs ataxia is a severe neurodegenerative disease caused by the decreased expression of frataxin, a mitochondrial protein that stimulates iron-sulfur (Fe-S) cluster biogenesis. In mammals, the primary steps of Fe-S cluster assembly are performed by the NFS1-ISD11-ISCU complex via the formation of a persulfide intermediate on NFS1. Here we show that frataxin modulates the reactivity of NFS1 persulfide with thiols. We use maleimide-peptide compounds along with mass spectrometry to probe cysteine-persulfide in NFS1 and ISCU. Our data reveal that in the presence of ISCU, frataxin enhances the rate of two similar reactions on NFS1 persulfide: sulfur transfer to ISCU leading to the accumulation of a persulfide on the cysteine C104 of ISCU, and sulfur transfer to small thiols such as DTT, L-cysteine and GSH leading to persulfuration of these thiols and ultimately sulfide release. These data raise important questions on the physiological mechanism of Fe-S cluster assembly and point to a unique function of frataxin as an enhancer of sulfur transfer within the NFS1-ISD11-ISCU complex.

Convergent solid phase peptide synthesis. I. Synthesis of protected segments on a hydroxymethylphenyloxymethyl resin using the base labile FMOC α-amine protection. Model synthesis of LHRH.

Abstract Convergent solid phase peptide synthesis has been applied to yield LHRH. The segments 1–6 and 7–10 of LHRH were synthesized on a hydroxymethylphenyloxymethyl resin using the base labile Fmoc protecting group on the α-amines. The side chains were protected by HF labile groups. Purification of the segments was performed on Sephadex LH-20 columns and by HPLC on Silica Gel 60 columns. The two segments were then assembled on an α-aminobenzyl resin to yield entire sequence of LHRH. After HF treatment and standard purification on Sephadex G-15 and carboxymethylcellulose CM-52 the desired LHRH was obtained. Synthesis of the segments by the same strategy on carbazoyloxymethylphenyloxymethyl resin showed up unexpected difficulties.

Towards nucleopeptides containing any trifunctional amino acid (II)

Abstract Nucleopeptides with no restriction in the amino acid composition can be synthesized using stepwise solid-phase methodology. Best conditions for the protection of arginine and cysteine, as well as for the final deprotection treatment are established, and our conclusions can be extended to the preparation of any peptide–oligonucleotide hybrid. The association between certain side reactions and nucleopeptide sequences is also discussed.

Maleimide-Dimethylfuran exo Adducts: Effective Maleimide Protection in the Synthesis of Oligonucleotide Conjugates

The reaction of maleimide-containing compounds with 2,5-dimethylfuran gives a mixture of exo and endo isomers from which the exo cycloadduct can be easily isolated taking advantage of its stability in concentrated aqueous ammonia. Bifunctional compounds incorporating a dimethylfuran-protected maleimide (exo adduct) have been attached to resin-linked oligonucleotide chains. Removal of protecting groups masking oligonucleotide functionalities followed by retro-Diels-Alder maleimide deprotection affords maleimido-oligonucleotides suitable for conjugation, as assessed by their reaction with different thiols.

Convergent solid phase peptide synthesis. v. synthesis of the 1-4, 32-34, and 53-59 protected segments of the toxin ii of androctonus australis hector.

Abstract Two protected peptide segments corresponding to the sequence 32-34 and 53-59 of toxin II of the north African scorpion Androctonus australis Hector have been synthesized on a photolabile Nbb-resin using the TFA-labile Boc α-amino protection and HF-labile side chain protecting groups. A third protected peptide corresponding to segment 1-4 has been synthesized on the same resin but with a t-butyl group for β protection of aspartic acid and a Z group on the lysine side chain. For this last segment a combination of Boc and Fmoc groups for α -amino protection has been used successfully on the Nbb-resin. After photolysis the crude peptides have been treated by solvent extraction and semi-preparative HPLC to yield highly purified segments. These syntheses show the flexibility of the convergent solid phase approach and how segments with different and independent protecting groups can be assembled by solid phase peptide procedure.

Criteria for the economic large scale solid-phase synthesis of oligonucleotides

Abstract The experimental conditions necessary for reducing the cost of large-scale solid-phase oligonucleotide synthesis by the phosphite triester approach have been studied using highly loaded polystyrene resins.

Synthesis of modified oligonucleotides containing 4-guanidino-2-pyrimidinone nucleobases

Abstract Oligonucleotides incorporating 4-guanidino-2-pyrimidinone nucleobases have been prepared. These nucleobase analogues were designed to mimic the double hydrogen bond donor pattern of protonated cytosines in parallel triple helices. Guanidine-, N-methyl-, N,N-dimethyl-, and N,N′-dimethylguanidine-containing nucleoside H-phosphonates were used for the synthesis of oligonucleotide analogues with minor modifications in standard solid-phase procedures.

Convergent solid phase peptide synthesis. VII: Good yields in the coupling of protected segments on a solid support

Abstract Protected peptides corresponding to the 64 amino acids of the whole sequence of toxin II of Androctonus australis Hector have been assembled on a solid support. Solid phase sequencing has proved to be extremely useful for the evaluation of the coupling yields, which have all been nearly quantitative.

AN IMPROVED SYNTHESIS OF N-[(9-HYDROXYMETHYL)-2-FLUORENYL]SUCCINAMIC ACID (HMFS), A VERSATILE HANDLE FOR THE SOLID-PHASE SYNTHESIS OF BIOMOLECULES

The optimization of a synthetic process for the preparation of HMFS handle, which is used for the solid-phase synthesis of peptides and oligonucleotides, is presented.