Showing papers by "Fernando Albericio published in 2002"
TL;DR: A new family of peptide dendrimers based on polyproline helices and cis-4-amino-L-proline as a branching unit and both linear and dendritic polyprolines were found to be actively internalized by rat kidney cells.
Abstract: 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.
106 citations
TL;DR: This study details a series of conditions that may be applied to ensure 'safe' incorporation of cysteine with minimal racemization during automated or manual solid-phase peptide synthesis.
Abstract: This study details a series of conditions that may be applied to ensure 'safe' incorporation of cysteine with minimal racemization during automated or manual solid-phase peptide synthesis. Earlier studies from our laboratories [Han et al. (1997) J. Org. Chem. 62, 4307-4312] showed that several common coupling methods, including those exploiting in situ activating agents such as N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-ylmethylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HATU), N-[1H-benzotriazol-1-yl)-(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HBTU), and (benzotriazol-1-yl-N-oxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) [all in the presence of N-methylmorpholine (NMM) or N,N-diisopropylethylamine (DIEA) as a tertiary amine base], give rise to unacceptable levels (i.e. 5-33%) of cysteine racemization. As demonstrated on the tripeptide model H-Gly-Cys-Phe-NH(2), and on the nonapeptide dihydrooxytocin, the following methods are recommended: O-pentafluorophenyl (O-Pfp) ester in DMF; O-Pfp ester/1-hydroxybenzotriazole (HOBt) in DMF; N,N'-diisopropylcarbodiimide (DIPCDI)/HOBt in DMF; HBTU/HOBt/2,4,6-trimethylpyridine (TMP) in DMF (preactivation time 3.5-7.0 min in all of these cases); and HBTU/HOBt/TMP in CH(2)Cl(2)/DMF (1:1) with no preactivation. In fact, several of the aforementioned methods are now used routinely in our laboratory during the automated synthesis of analogs of the 58-residue protein bovine pancreatic trypsin inhibitor (BPTI). In addition, several highly hindered bases such as 2,6-dimethylpyridine (lutidine), 2,3,5,6-tetramethylpyridine (TEMP), octahydroacridine (OHA), and 2,6-di-tert-butyl-4-(dimethylamino)pyridine (DB[DMAP]) may be used in place of the usual DIEA or NMM to minimize cysteine racemization even with the in situ coupling protocols.
68 citations
TL;DR: In this article, the authors address some of the important issues that arise when outsourcing chemistry duing the discovery/development phase of a new chemical entity and present a solution to solve them.
Abstract: Vendors and purchasers have different agendas when outsourcing custom chemical services. The forces that motivate the people who purchase chemical services are different from those that motivate custom chemistry providers. This article addresses some of these important issues that arise when outsourcing chemistry duing the discovery/development phase of a new chemical entity.
36 citations
TL;DR: In this paper, a side-reaction consisting of premature and undesired removal of the Fmoc group has been detected in solid-phase peptide synthesis, which can be caused by a primary amine of sufficient basicity, such as the e-amino of the Lys, present in the peptide resin.
30 citations
27 citations
TL;DR: The results obtained suggest that β12–28 behaviour is comparable to that of the natural β‐amyloid protein although kinetically slower, although a lack of reproducibility was observed in the dose‐response experiments.
Abstract: 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.
21 citations
TL;DR: In this article, a four-dimensional orthogonal protecting scheme that involves the acid-labile BAL linker in conjunction with Fmoc, Alloc and pNb protecting groups, which can be removed by β-elimination, allyl transfer, and reductive hydrolysis, respectively, allows the solid phase preparation of scaffolds based on a cyclic tetra-β-peptide with free amino side chains ready for further elaboration.
20 citations
TL;DR: This approach provides a new method for the synthesis of other repetitive branched peptides, minimizing not only synthetic difficulties but also purification problems.
15 citations
TL;DR: In this paper, a solid-phase synthesis of N -substituted carbamates using the trisalkoxy)benzyl (BAL) resin is reported.
15 citations
TL;DR: A variety of Fmoc-protected amino ketones have been prepared in good yields from amino acids by their transformation into thioesters of 2-mercaptopyridine and reaction of the resulting products with dialkylcuprates as mentioned in this paper.
13 citations
TL;DR: A reappraisal of the use of the water-soluble carbodiimide/CuCl method for the preparation of this kind of peptide in both solution and solid-phase modes is reported and some side reactions encountered during the process are described.
Abstract: α, β-Didehydroamino acids, which are key components of both natural andde novo peptides, are frequently encountered in naturally occurring peptides — mostly of microbial and fungal origin and/or from marine organisms. Herein, we report on a reappraisal of the use of the water-soluble carbodiimide/CuCl method for the preparation of this kind of peptide in both solution and solid-phase modes and describe some side reactions encountered during the process.
TL;DR: In this article, a demonstration library of α,α-disubstituted-α-acylaminoketones, of interest as ecdysone agonists, is described.
TL;DR: The data show a direct correlation between anti-viral activity and the ability of the peptides to interfere with maturation of the Env precursors, and it is shown 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.
Abstract: 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.
TL;DR: In this article, solid phase synthesis of prototypical α-acylamino-α,α-disubstituted ketones on two different solid supports is described, in both cases the ketone was formed by reaction of a Grignard reagent with an N-acyl-α disubstitized amino acid immobilized through its carboxylate as a Weinreb amide derivative.
01 Jan 2002
TL;DR: The thiouronium salts S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylhexafluorophosphate (HOTT) and tetrafluoroborate (TOTT) have been employed as reagents in solution and solid-phase peptide coupling chemistry as discussed by the authors.
Abstract: The thiouronium salts S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouronium hexafluorophosphate (HOTT) and tetrafluoroborate (TOTT), and S-(1-oxido-2-pyridinyl)-1,3-dimethyl-1,3-trimethylenethiouronium hexafluorophosphate (HODT) and tetrafluoroborate (TODT), prepared from 2-mercaptopyridine-1-oxide and 1,1,3,3-tetramethylurea (TMU) or 1,3-dimethylpropyleneurea (DMPU), have been employed as reagents in solution and solid-phase peptide coupling chemistry. Furthermore, 2-mercaptopyridine-1-oxide has been employed as racemization-reducing additive combined with the new thiouronium salts and other frequently used peptide coupling reagents such as DCC or TBTU.
01 Jan 2002
01 Jan 2002
01 Jan 2002
TL;DR: This work presents an extension of the recently described BAL approach to accommodate C-terminal moieties that are labile to bases, e.g., piperidine (as used in Fmoc chemistry), or to circumvent other synthetic difficulties, i.e., due to steric hindrance of the modification.
Abstract: Our recently described BAL approach [1] has been used by us and others for the rapid and efficient preparation of C-terminal modified peptides and small organic molecules. We present here an extension of this work to accommodate C-terminal moieties that are labile to bases, e.g., piperidine (as used in Fmoc chemistry), or to circumvent other synthetic difficulties, e.g., due to steric hindrance of the modification.
01 Jan 2002
TL;DR: The main advantage of this approach consists of the possibility to generate, directly, peptide fragments with modifications at the C-terminus position (amides, esters), which have potential interest for therapeutical use.
Abstract: Although the solid-phase peptide synthesis in the conventional C N direction is widely used and developed, few attempts have been mentioned for peptide assembly in the reverse N C direction [1,2]. The main advantage of this approach consists of the possibility to generate, directly, peptide fragments with modifications at the C-terminus position (amides, esters). C-terminal modified peptides, which are abundant in nature, have potential interest for therapeutical use. Furthermore, they could be readly engaged in a fragment condensation process.
01 Jan 2002
TL;DR: In this article, the serine residues in the center of the sequence are a necessary requirement for trimer formation which results from destabilization of the helical parallel cyclic dimer.
Abstract: Oxidation in the presence of TFE of several [19]- or [20]-peptides with two cysteine residues in positions i, i+17 and with two serine residues at positions i+8 and i+9 leads to the spontaneous formation, in high yields, of cyclic disulfide bonded trimers in which two of the chains are parallel and the third one is antiparallel. The serine residues in the center of the sequence are a necessary requirement for trimer formation which results from destabilization of the helical parallel cyclic dimer.