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Biomedical subjects

Fernando Albericio

Publications and source records attributed to Fernando Albericio.

51 records · Page 3Linked to original sources
PubMed2003

Qualitative colorimetric tests for solid phase synthesis.

Results obtained in the application of these tests are summarized in Table II. We have encountered some variations in the reproducibility and accuracy of some tests. Due to the numerous factors that can influence colorimetric test results (e.g., test reagent stability, resin type, functional group interference, and lability of protecting group) we highly recommend performing a positive and a negative control for any test applied to a new synthesis. We also emphasize the importance of reagent solution purity on the outcome of test results, hence we strongly encourage the use of correctly prepared and carefully stored reactants. To minimize false results due to lability of the resin-product bond or the product itself (such as Fmoc-protected amino acids), colorimetric tests should be performed with the utmost immediacy in regards to completion of the step to be monitored. Hence the storage of resin over long periods of time (more than 24 h) before testing is not advisable. When the result of a colorimetric test is in doubt we advise repeating the test a few times until a reproducible result is obtained. The use of multiple tests for the same functional group may elucidate ambiguous or otherwise challenging cases.

Alcohols↗
PubMed2003

Exploring solid-phase approaches for the preparation of new beta-lactams from amino acids.

Two solid-phase approaches, involving the base-assisted intramolecular alkylation of N-chloroacetyl-Phe derivatives anchored to appropriate solid supports, were investigated for the preparation of novel beta-lactams. When a BAL-type strategy was used, the resin-bound azetidinones were easily formed, as established by MAS-NMR, but final compounds could not be removed from the resin, unless a suitable two linkers system was used. In the second approach, in which the Phe residue is anchored to a Wang-type resin through the carboxylate group, the corresponding 1,4,4-trisubstituted 2-azetidinone was obtained in moderate to good yield and high purity.

Amino Acids↗
PubMed2002

Effects of L- and D-REKR amino acid-containing peptides on HIV and SIV envelope glycoprotein precursor maturation and HIV and SIV replication.

The aim of the present study was to evaluate the capacity of synthetic l- and d-peptides encompassing the HIV-1(BRU) gp160 REKR cleavage site to interfere with HIV and simian immuno-deficiency virus (SIV) replication and maturation of the envelope glycoprotein (Env) precursors. To facilitate their penetration into cells, a decanoyl (dec) group was added at the N-terminus. The sequences synthesized included dec5d or dec5l (decREKRV), dec9d or dec9l (decRVVQREKRV) and dec14d or dec14l (TKAKRRVVQREKRV). The peptide dec14d was also prepared with a chloromethane (cmk) group as C-terminus. Because l-peptides exhibit significant cytotoxicity starting at 35 microM, further characterization was conducted mostly with d-peptides, which exhibited no cytotoxicity at concentrations higher than 70 microM. The data show that only dec14d and dec14dcmk could inhibit HIV-1(BRU), HIV-2(ROD) and SIV(mac251) replication and their syncytium-inducing capacities. Whereas peptides dec5d and dec9d were inactive, dec14dcmk was at least twice as active as peptide dec14d. At the molecular level, our data show a direct correlation between anti-viral activity and the ability of the peptides to interfere with maturation of the Env precursors. Furthermore, we show that when tested in vitro the dec14d peptide inhibited PC7 with an inhibition constant K(i)=4.6 microM, whereas the peptide dec14l preferentially inhibited furin with a K(i)=28 microM. The fact that PC7 and furin are the major prohormone convertases reported to be expressed in T4 lymphocytes, the principal cell targets of HIV, suggests that they are involved in the maturation of HIV and SIV Env precursors.

Antiviral Agents↗
PubMed2002

Peptide dendrimers based on polyproline helices.

We present a new family of peptide dendrimers based on polyproline helices and cis-4-amino-L-proline as a branching unit. Dendrimers were synthesized by a convergent solid-phase peptide synthesis approach. The conformational transition between polyproline type I helix and polyproline type II helix was observed by circular dichroism in branched polyproline building blocks with more than 14 proline residues and in the resulting dendrimers. Both linear and dendritic polyprolines were found to be actively internalized by rat kidney cells. Preliminary results show that the antibiotic ciprofloxacin form complexes with branched polyproline chains in 99.5% propanol.

Animals↗
PubMed2002

Structural, kinetic and cytotoxicity aspects of 12-28 beta-amyloid protein fragment: a reappraisal.

A chemical, structural and biological study on the beta-amyloid peptide beta12-28 is reported which was carried out in order to assess the feasibility using this peptide fragment as a model of the natural beta-amyloid protein. The aggregation properties of beta12-28 have been investigated by pulse field-gradient NMR spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The results obtained suggest that beta12-28 behaviour is comparable to that of the natural beta-amyloid protein although kinetically slower. Translational diffusion coefficients obtained by NMR on an aged beta12-28 solution suggest that the soluble peptide fraction is composed of oligomeric intermediates adopting an extended ellipsoidal assembly rather than a spherical one. The beta12-28 peptide proved to be cytotoxic in PC12 cell cultures as monitored by the MTT assay, although a lack of reproducibility was observed in the dose-response experiments.

Amino Acid Sequence↗
PubMed1999

Backbone Amide Linker (BAL) Strategy for N(alpha)()-9-Fluorenylmethoxycarbonyl (Fmoc) Solid-Phase Synthesis of Unprotected Peptide p-Nitroanilides and Thioesters(1).

A novel and general backbone amide linker (BAL) strategy has been devised for preparation of C-terminal modified peptides containing hindered, unreactive, and/or sensitive moieties, in concert with N(alpha)()-9-fluorenylmethoxycarbonyl (Fmoc) solid-phase synthesis protocols. This strategy comprises (i) start of peptide synthesis by anchoring the penultimate residue, with its carboxyl group orthogonally protected, through the backbone nitrogen, (ii) continuation with standard protocols for peptide chain elongation in the C --> N direction, (iii) selective orthogonal removal of the carboxyl protecting group, (iv) solid-phase activation of the pendant carboxyl and coupling with the desired C-terminal residue, and (v) final cleavage/deprotection to release the free peptide product into solution. To illustrate this approach, several model peptide p-nitroanilides and thioesters have been prepared in excellent yields and purities, with minimal racemization. Such compounds are very difficult to prepare by standard Fmoc chemistry, including the BAL strategy as originally envisaged.

Journal Article↗
PubMed1997

Occurrence and Minimization of Cysteine Racemization during Stepwise Solid-Phase Peptide Synthesis(1)(,)(2).

Contrary to the conventional wisdom of the peptide synthesis field, N,S-protected derivatives of cysteine can undergo substantial levels of racemization with widely-used reagents and protocols for stepwise incorporation. A systematic study of this problem has been carried out as a function of coupling conditions and beta-thiol protecting groups, i.e., S-acetamidomethyl (Acm), S-triphenylmethyl (trityl or Trt), S-2,4,6-trimethoxybenzyl (Tmob), and S-9H-xanthen-9-yl (Xan), taking advantage of a convenient and quantitative model system assay involving HPLC resolution of H-Gly-L-Cys-Phe-NH(2) from H-Gly-D-Cys-Phe-NH(2). For example, standard protocols for couplings mediated by phosphonium and aminium salts, e.g., (benzotriazolyloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP), N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HBTU), N-[[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-yl]methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HATU), and (7-azabenzotriazol-1-yloxy)tris(pyrrolidino)phosphonium hexafluorophosphate (PyAOP), typically involve 5-min preactivation times and are conducted in the presence of suitable additives such as 1-hydroxybenzotriazole (HOBt) or 7-aza-1-hydroxybenzotriazole (HOAt) plus a tertiary amine base such as N,N-diisopropylethylamine (DIEA) or N-methylmorpholine (NMM). Under such conditions, the levels of racemization in the model peptide, expressed as the ratio of D:L peptide formed, were in the entirely unacceptable range of 5-33%. However, these levels were in general reduced by a factor of 6- or 7-fold by avoiding the preactivation step. Additional strategies to reduce racemization involved change to a weaker base, with 2,4,6-trimethylpyridine (TMP, collidine) being substantially better than DIEA or NMM; 2-fold reduction in the amount of base; and change in solvent from neat N,N-dimethylformamide (DMF) to the less polar CH(2)Cl(2)-DMF (1:1). Coupling methods for the safe incorporation of cysteine with minimal racemization (<1% per step) in 9-fluorenylmethyloxycarbonyl (Fmoc) solid-phase peptide synthesis include BOP (or HBTU or HATU)/HOBt (or HOAt)/TMP (4:4:4) without preactivation in CH(2)Cl(2)-DMF (1:1), DIPCDI/HOBt (or HOAt) (4:4) with 5-min preactivation, and preformed pentafluorophenyl (Pfp) esters in CH(2)Cl(2)-DMF (1:1).

Journal Article↗
PubMed1997

Total Synthesis of Dehydrodidemnin B. Use of Uronium and Phosphonium Salt Coupling Reagents in Peptide Synthesis in Solution.

New total syntheses of didemnin A and of dehydrodidemnin B are described. The latter didemnin has the highest antiproliferative activity of all members of this family of macrocyclic depsipeptides. It was produced on coupling the side chain Pyr-Pro-OH to didemnin A, which was itself synthesized by two novel routes. One of these was based on the elaboration of a linear heptadepsipeptide incorporating the first amino acid of the didemnin side chain, (R)-N(Me)-Leu. Deprotection of the amino and carboxyl terminii of this linear precursor followed by macrocyclization gave a protected derivative of didemnin A. The second route involved synthesis of the Boc-protected didemnin macrocycle from a linear hexadepsipeptide lacking (R)-N(Me)-Leu. Removal of the Boc group from the macrocycle followed by its coupling with Boc-(R)-N(Me)-Leu-OH then gave Boc-didemnin A. The overall yield was much higher for the second strategy (27% compared to 4% for the first synthesis), but both allowed synthetic didemnin A, identical with a natural sample, to be prepared. Extensive use was made of phosphonium and uronium salt-based coupling reagents, such as BOP, PyBrOP, PyAOP, HBTU, and HATU for the formation of both the secondary and tertiary amide bonds present in these complex depsipeptides.

Journal Article↗
PubMed1996

Preparation and Applications of Xanthenylamide (XAL) Handles for Solid-Phase Synthesis of C-Terminal Peptide Amides under Particularly Mild Conditions(1-3).

[[9-[(9-Fluorenylmethyloxycarbonyl)amino]xanthen-2(or 3)-yl]oxy]alkanoic acid (XAL) handles have been prepared by efficient four-step routes from 2- or 3-hydroxyxanthone and coupled onto a range of amino-functionalized supports. The resultant XAL supports are the starting points for solid-phase peptide synthesis by Fmoc chemistry. Upon completion of chain assembly, C-terminal peptide amides are released in excellent yields and purities by use of low concentrations [1-5% (v/v)] of trifluoroacetic acid (TFA) in dichloromethane, often without a need for added carbocation scavengers. These cleavage conditions allow retention of all or a significant portion of tert-butyl type and related side-chain protecting groups, which subsequently may be removed fully in a solution process carried out at higher acid concentration. XAL supports are particularly useful for the synthesis of acid-sensitive peptides, including tryptophan-containing sequences that are known to be susceptible to yield- and/or purity-reducing alkylation side reactions. The effectiveness of this chemistry was shown with the syntheses of prothrombin (1-9), acyl carrier protein (65-74), Tabanus atratus adipokinetic hormone, fragments of the protein RHK 1, CCK-8 sulfate, and oxytocin. Furthermore, the application of XAL supports for the preparation of fully protected peptide amides has been demonstrated.

Journal Article↗
PubMedDate not supplied

A comparative study of different presentation strategies for an HIV peptide immunogen.

Different strategies have been used to increase the immunogenicity of an antigenic HIV peptide as a vaccine candidate. The selected B-cell epitope comprises 15 amino acids (317-331) of the V3 region of HIV-1, JY1 isolate (subtype D), in tandem with a T-helper epitope corresponding to the 830-844 region of tetanus toxoid. Several presentations, including oligomerization, multiple antigenic peptide dendrimers, and conjugation to dextran beads or to other macromolecular carriers, have been synthesized and evaluated. Murine sera from the different presentations of the V3 epitope have been compared with regard to antibody titers and cross-reactivity with heterologous HIV subtypes. The dendrimer version of the peptide conjugated to HBsAg protein was a better immunogen than the dendrimer alone and showed a higher immunogenicity than other multimeric presentations or than the peptide alone conjugated to dextran. The dendrimer version, either alone or conjugated to HBSAg, enhanced cross-reactivity toward heterologous V3 sequences relative to monomeric peptide. In addition, fine epitope mapping of the entire JY1 sequence by sera from the different immunization groups was performed by the spot synthesis technique. Results showed that the amino acids involved in molecular recognition were LXQXXY or LXQXLY, with particularly strong recognition of the C-terminal region LGQALY. However, cross-reactivity toward the heterologous sequences did not completely correlate with recognition of particular amino acids in the primary sequences. These results can find application in the development of HIV vaccine candidates.

AIDS Vaccines↗
PubMedDate not supplied

Bicyclic homodetic peptide libraries: comparison of synthetic strategies for their solid-phase synthesis.

Preliminary studies and synthesis development for the preparation of a bicyclic homodetic peptide library have been carried out using orthogonal protection schemes. The best results have been obtained using two Fmoc/tBu-based strategies, in which the first cycle is carried out in the solid phase through side chain functional groups previously protected with Aloc/Al groups. The second cycle is performed either in the solid phase, which requires side chain anchoring of a trifunctional amino acid and Dmb protection for the C-terminus carboxyl group, or in solution, which requires the use of highly labile resins, such as the 2-chlorotrityl (Barlos) resin. Only when the cycles are formed in a ziplike manner, that is, first the small cycle and then the larger ring, is the desired final product obtained.

Bridged Bicyclo Compounds↗
PubMedDate not supplied

Multicomponent reactions with dihydroazines: efficient synthesis of a diverse set of pyrido-fused tetrahydroquinolines.

A multicomponent assembly of pyrido-fused tetrahydroquinolines is accomplished in a one-pot process from the interaction of dihydroazines, aldehydes, and anilines. A rational screening of the different components and parameters of this reaction, such as the range of reactive starting materials, catalysts and reaction conditions (solvent range; thermal, high pressure- and microwave-promoted processes) is carried out. Optimized conditions allow an efficient preparation of pyrido-fused tetrahydroquinolines with good yields, bypassing the biomimetic NADH-like reductive pathway which is typical in the interaction of dihydropyridines with carbonyl compounds and amines. Furthermore, solid-supported versions of the process have been developed, which should facilitate the preparation of libraries.

Aldehydes↗
PubMedDate not supplied

ChemMatrix, a poly(ethylene glycol)-based support for the solid-phase synthesis of complex peptides.

CM (ChemMatrix) resin is a new, totally poly(ethylene glycol) (PEG)-based resin, made exclusively from primary ether bonds and, therefore, highly chemically stable. It exhibits good loading and is user-friendly because of its free-flowing form upon drying. It performs excellently for the preparation of hydrophobic, highly structured, and poly-Arg peptides, as compared to polystyrene (PS) resins. In the most striking example, stepwise solid-phase assembly of the highly complex beta-amyloid (1-42) peptide resulted in a crude material of 91% purity. In contrast, literature procedures using PS or PEG-PS-based resins for this peptide required convergent approaches, additional time-consuming steps, or both. In addition to the difficulties of its synthesis, characterization of the beta-amyloid (1-42) peptide as a monomer is also a challenge, and methods for characterization by HPLC and MALDI-TOF have also been developed.

Amyloid beta-Peptides↗