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PubMed2004

Dipeptide boronic acid, a novel proteasome inhibitor, prevents islet-allograft rejection.

BACKGROUND: We have demonstrated previously in vitro that proteasome inhibitors suppress the proliferation, and induce the apoptosis, of activated T cells. This implies that they could be used as a novel category of immunosuppressants to block allograft rejection. Therefore, in this study, dipeptide boronic acid (DPBA) was tested for its effect on mouse islet transplantation. METHODS: First, DPBA was investigated in vitro for its effect on mouse mixed lymphocyte reaction (MLR) and cytotoxic T-lymphocyte (CTL) activity. DPBA was then used in vivo to treat mouse islet-allograft rejection. RESULTS: Both MLR and CTL were dose dependently suppressed by the proteasome inhibitor. A 17-day DPBA regimen resulted in islet-allograft survival in 50% of the recipients for a duration of up to 60 days, whereas the control group without immunosuppressants rejected the islet graft in 7 days. DPBA showed moderate side effects according to blood biochemistry; the function of endogenous islets after treatment appeared normal on glucose challenge. CONCLUSIONS: The proteasome inhibitor could inhibit islet-allograft rejection in mice without serious side effects at therapeutic dose levels. This has opened a new dimension in the development of better immunosuppression regimens for islet transplantation.

Animals↗
PubMed2003

Neuroprotective and nootropic actions of a novel cyclized dipeptide after controlled cortical impact injury in mice.

1-ARA-35b (35b) is a cyclized dipeptide that shows considerable neuroprotective activity in vitro and improves neurologic recovery after fluid percussion-induced traumatic brain injury in rats. The authors evaluated the effects of treatment with 35b in mice subjected to controlled cortical impact brain injury. Animals treated with intravenous 35b after traumatic injury showed significantly enhanced recovery of beam walking and place learning functions compared with vehicle-treated controls, in addition to reduced lesion volumes. Beneficial effects were dose related and showed an inverted U-shaped dose-response curve between 0.1 and 10 mg/kg. Protective actions were found when the drug was administered initially at 30 minutes or 1, 4, or 8 hours, but not at 24 hours, after trauma. In separate experiments, rats treated with 35b on days 7 through 10 after injury showed remarkably improved place learning in comparison with injured controls. These studies confirm and extend the neuroprotective effects of this diketopiperazine in traumatic brain injury. In addition, they show that 35b has a relatively wide therapeutic window and improves cognitive function after both acute and chronic injury.

Animals↗
PubMed2000

A silaproline-containing dipeptide.

The silaproline-containing dipeptide N-(3, 3-dimethyl-1-pivaloyl-1-aza-3-sila-5-cyclopentylcarbonyl)-L- alanine isopropylamide, C(17)H(33)N(3)O(3)Si, has two independent molecules in the asymmetric unit and each adopts a beta-II folded conformation, where the amide on the terminal C interacts intramolecularly with the pivaloyl O atom. The five-membered silaproline ring is C(beta)-puckered, an infrequent conformation for the homologous proline ring.

Crystallography, X-Ray↗
PubMed2003

L-methionyl-L-alanine: a dipeptide with hexagonal symmetry and Z' = 7.

The crystal structure of L-methionyl-L-alanine, C(8)H(16)N(2)O(3)S, is very similar to that of L-valyl-L-alanine [Görbitz & Gundersen (1996). Acta Cryst. C52, 1764-1767] and other related dipeptides in space group P6(1), but there are seven molecules in the asymmetric unit. The Z value of 42 is the highest ever observed for a chiral molecule.

Alanine↗
PubMed2004

A crystallographic titration of the dipeptide L-isoleucyl-L-isoleucine.

The dipeptide L-Ile-L-Ile has been crystallized in four different protonation states, including as a cation, a zwitterion and an anion, as well as a dimeric cation in which two peptide molecules, linked by a strong -COO...H...OOC- hydrogen bond, share an overall positive charge of +1. This unprecedented series of crystal structures exhibits differences in hydrogen-bonding capabilities, conformational properties and molecular packing arrangements. The crystallization of L-Ile-L-Ile as an anion was achieved by slow evaporation from an NH(3)(l) solution to give the first ever ammonium salt of a peptide (or amino acid).

Anions↗
PubMed1991

Transcriptional regulation of a Bacillus subtilis dipeptide transport operon.

The Bacillus subtilis dciA operon, which encodes a dipeptide transport system, was induced rapidly by several conditions that caused the cells to enter stationary phase and initiate sporulation. The in vivo start point of transcription was mapped precisely and shown to correspond to a site of transcription initiation in vitro by the major vegetative form of RNA polymerase. Post-exponential expression was prevented by a mutation in the spo0A gene (whose product is a known regulator of early sporulation genes) but was restored in a spo0A abrB double mutant. This implicated AbrB, another known regulator, as a repressor of dciA. In fact, purified AbrB protein bound to a portion of the dciA promoter region, protecting it against DNase I digestion. Expression of dciA in growing cells was also repressed independently by glucose and by a mixture of amino acids; neither of these effects was mediated by AbrB.

Adenosine↗
PubMed1982

Synthesis and biological activity of some new 3,6-dinitro-1:8-naphthaloyl- and 3,6-diamino-1:8-naphthaloylamino acids and dipeptide derivatives.

Synthesis of a series of 3,6-dinitro-1:8-naphthaloylamino acids (II-IX) and some of their corresponding methyl esters (X-XVI) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXVI) is described. Coupling of 3,6-dinitro-1:8-naphthaloylamino acids with amino acid methyl ester hydrochlorides in dioxane-DMF-Et3N medium using DCC method furnishes the desired 3,6-dinitro-1:8-naphthaloyldipeptide methyl esters (XVII-XXVIII). Most of the synthesized 3,6-dinitro-1:8-naphthaloylamino acids, esters and dipeptide derivatives (compounds III-VI, XI-XV, XVII, XIX-XXI, XXIII and XXV) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXV) were found to be active against a number of microorganisms.

Amino Acids↗
PubMed1985

Theoretical pi-pi* absorption and circular dichroic spectra of cyclic dipeptides.

The dipole interaction model, treated by the partially dispersive normal mode method, is used to calculate circular dichroic spectra of cyclo(Gly-Gly), cyclo (Ala-Gly), cyclo(Ala-Ala), cyclo(Pro-Gly), cyclo(Pro-Ala), cyclo(Pro-Val), cyclo (Pro-D-Val), and cyclo(Pro-Pro) in the amide pi-pi* absorption band near 190 nm. Assuming a standard backbone geometry, spectra which are in fair to good agreement with experiment are obtained for these molecules. The spectra are predicted to be sensitive to conformations of Pro and Val side chains. The effects of dipeptide ring folding on calculated CD spectra are mostly consistent with those found by other workers, except that it is found that a planar ring conformation of cyclo (Ala-Ala) and cyclo (Ala-Gly) gives predicted spectra comparable to experiment. The same model gives theoretical absorption spectra consistent with available experimental data.

Chemical Phenomena↗
PubMed1987

Cyclopropane amino acid ester dipeptide sweeteners.

A series of esters of L-aspartyl-1-aminocyclopropane carboxylic acid has been prepared and their sweet tastes determined. The sweetest ester prepared was about 300 times sweeter than sucrose. An attempt to use basic conditions during preparation of the dipeptide allyl ester led to succinimide formation of the aspartyl peptide even though the beta-carboxyl group was protected by a t-butyl ester function. The X-ray structure of the propyl ester (1c) was determined and its conformation is discussed.

Aspartame↗
PubMed1987

Amino acids and peptides. XVIII. Dipeptide formation during the synthesis of Z-Asp(OBzl)-OH.

During the benzyloxycarbonylation of H-Asp(OBzl)-OH by the Schotten-Bauman reaction with benzyloxycarbonyl chloride in the presence of NaHCO3 or Na2CO3, besides Z-Asp(OBzl)-OH, Z-Asp(OBzl)-Asp(OBzl)-OH was formed as side product, although the extent of the dipeptide formation differed depending on the base used (10% and 20% respectively). It was found that melting point, rotation value and Rf values upon thin-layer chromatography of Z-Asp(OBzl)-Asp(OBzl)-OH were quite similar to those of Z-Asp(OBzl)-OH.

Amino Acids↗
PubMed1988

Potential energy calculations on phenylalanine rotamers in different boat forms of proline-containing cyclic dipeptides.

Previous potential energy calculations have always indicated that the folded conformation is the most stable one for cyclic dipeptides containing benzylic side chains. We have carried out intramolecular van der Waals potential energy calculations on cyclo-(D-Phe-L-Pro), N-(N-phenylacetyl-L-alanyl)-cyclo-(L-Phe-D-Pro) and N-(pyruvoyl)-cyclo-(L-Phe-D-Pro) adopting the geometries found in their crystal structures. The calculations made on these compounds, having the peptide skeleton made of the same aminoacid residues but differing in the degree of buckling of the boat, show that there is a dependence between diketopiperazine ring and phenylalanine side-chain conformations. The folded conformer is preferred as long as it is allowed by the degree of buckling of the boat. When the boat becomes highly buckled, as in the case of the pyruvoyl derivative, the folded rotamer is no longer favoured. This is the first energy calculation to demonstrate that the folded rotamer is not always the most stable one.

Dipeptides↗
PubMed1989

Enkephalin-degrading enzyme inhibitors. Crucial role of the C-terminal residue on the inhibitory potencies of retro-hydroxamate dipeptides.

The retro-inversion of the amide bond in kelatorphan and analogs, the first series of complete inhibitors of enkephalin metabolism, led to compounds highly efficient only against the neutral endopeptidase 24-11 (NEP). In order to increase the recognition of the aminopeptidase N (APN) and dipeptidylaminopeptidase (DAP), without loss of affinity for NEP, the malonyl group of these retro-inhibitors was replaced by diversely substituted succinyl moieties. All the molecules synthesized are highly efficient NEP inhibitors with Ki's in the 0.2-1 nM range, indicating that NEP possesses a relatively large and not very selective S'2 subsite. In contrast, inhibition of DAP activity is crucially dependent on the size and the position of the substituent in the succinyl moiety. Inhibitory potencies in the nanomolar range are obtained with compounds containing a benzyl group in the alpha-position related to the retro amide bond. Finally, a relatively modest inhibition of APN was observed with Ki's in the 0.5-1 microM range for compounds with benzyl or cyclohexyl group in P'2 position. However, these data demonstrate that efficient and complete inhibition of enkephalin degradation can be obtained with hydroxamate dipeptides containing a retro amide bond. The analgesic potency of the most active inhibitors was measured using the hot plate test in mice. Significant antinociceptive responses were obtained but these effects were rather weaker than those expected from the in vitro inhibitory potencies of these compounds on the three enkephalin-degrading enzymes.

Animals↗
PubMed1990

Enzymatic synthesis of dipeptide units of the D-D-configuration in aqueous media.

The enzymatic synthesis of dipeptide units of the D-D-configuration in aqueous media, catalysed by muramoyl-pentapeptide carboxypeptidase (E.C.3.4.17.8), is described. Ac-L-Lys(Ac)-D-Ala-D-Lac-OH and Ac-D-Ala-OMe were used as acyl-components. Neutral, basic, and hydrophobic amino acids acting as nucleophiles were incorporated. The enzyme is stereospecific in that only the D-enantiomers of amino acids or amino acid derivatives were incorporated. As nucleophiles, the unmodified amino acids resulted in higher product yields compared with using the corresponding amino acid derivatives. Product yields ranged from 40 to 87%.

Amino Acid Sequence↗
PubMed1991

Synthesis, crystal structure and molecular conformation of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr alpha,beta-unsaturated dipeptide.

The crystal structure of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr dipeptide has been solved by X-ray diffraction. The peptide crystallizes in monoclinic space group P2(1)/c with a = 13.445 (3) A, b = 35.088 (4) A, c = 14.755 (3) A, beta = 116.73 (1) degree, Z = 12 and dc = 1.151 g.cm-3. The three independent molecules per asymmetric unit accommodate a beta II-folded conformation, but only one of them contains the typical i + 3----i interaction characterizing a beta-turn. In the other two molecules, the N...O distance exceeds 3.2 A, a value generally considered the upper limit for hydrogen bonds in peptides. In solution, the beta II-turn conformation is largely predominant.

Dipeptides↗
PubMed1991

Preparations, solution conformation and molecular structures of N,N'-ethylene-bridged dipeptides and their derivatives.

The solution conformations of novel dipeptides, methyl (2S, 3'S)-3-methyl-2-(2'-oxo-3'-isopropyl-1'-piperazinyl)-butanoate (EVV-OCH3), methyl (2S, 3'S)-3-phenyl-2-(2'-oxo-3'-benzyl-1'-piperazinyl) propionate (EFF-OCH3), and their derivatives (Boc-Gly-EVV-OH, Boc-Gly-EVV-Gly-OH, and Boc-Gly-EFF-OH), were studied by 1H NMR measurements and molecular mechanics calculations (1). The molecular structures of Boc-Gly-EVV-OH, Boc-Gly-EFF-OH, and the hydrochloride of EVV-OCH3 were determined by X-ray analyses. The conformations of the piperazinone rings and the side chains of these oligopeptides were clarified.

Chemical Phenomena↗
PubMed1991

Synthesis of histidine-containing dipeptide affinity-labelling agents. Relative inactivation rates of cathepsins B and L.

Peptidyl diazomethyl ketones and fluoromethyl ketones containing histidine in the C-terminal position were synthesized to determine their properties as proteinase inactivators. These were examined chiefly with derivatives of Z-Ala-His. The protection of histidine during conversion of the C-terminal residue to the diazomethyl ketone required unblocking conditions which avoid acid due to the lability of this function. This was achievable with a Cbz-imidazole derivative since aminolysis provided deblocking without disturbance of the diazomethyl ketone function. In the case of the fluoromethyl ketone synthesis using fluoroacetic anhydride (Dakin-West procedure), the desired product could be isolated without ring blocking. The Z-Ala-His products showed enhanced selectivity for inactivation of cathepsin B over L when compared to analogous dipeptide inhibitors.

Affinity Labels↗