Acid catalysis in the formation of dioxopiperazines from peptides containing tetrahydroisoquinoline-3-carboxylic acid at position 2

Stability of protein pharmaceuticals: an update

In 1989, Manning, Patel, and Borchardt wrote a review of protein stability (Manning et al., Pharm. Res. 6:903-918, 1989), which has been widely referenced ever since. At the time, recombinant protein therapy was still in its infancy. This review summarizes the advances that have been made since then regarding protein stabilization and formulation. In addition to a discussion of the current understanding of chemical and physical instability, sections are included on stabilization in aqueous solution and the dried state, the use of chemical modification and mutagenesis to improve stability, and the interrelationship between chemical and physical instability.

Solid-phase synthetic strategy and bioevaluation of a labeled delta-opioid receptor ligand Dmt-Tic-Lys for in vivo imaging

A general solid-phase synthetic strategy is developed to prepare fluorescent and/or lanthanide-labeled derivatives of the delta-opioid receptor (deltaOR) ligand H-Dmt-Tic-Lys(R)-OH. The high delta-OR affinity (K(i) = 3 nM) and desirable in vivo characteristics of the Cy5 derivative 1 suggest its usefulness for structure-function studies and receptor localization and as a high-contrast noninvasive molecular marker for live imaging ex vivo or in vivo.

New di-(beta-chloroethyl)-alpha-amides on N-(meta-acylamino-benzoyl)- D,L-aminoacid supports with antitumoral activity

In order to obtain new compounds with antitumoural action the N-(meta-acylaminobenzoyl)-alpha-acylaminobenzoyl)-alpha-aminoacids 4-9 were prepared. These compounds were subsequently converted into the corresponding Delta(2)-oxazolin-5-ones 10-15, which in turn were submitted to a ring opening reaction with di-(beta-chloroethyl)amine to afford the peptide supported N-mustards 16-21, which showed low toxicity and cytostatic activity similar to that of sarcolisine against the Ehrlich ascite and Walker 253 carcinosarcoma.

Dmt-Tic-NH-CH2-Bid (UFP-502), a potent DOP receptor agonist: in vitro and in vivo studies

Knockout and pharmacological studies demonstrated that the activation of delta opioid peptide (DOP) receptors produces antidepressant-like effects in rodents. Here we report the results obtained with the novel DOP ligand H-Dmt-Tic-NH-CH(2)-Bid (UFP-502). UFP-502 bound with high affinity (pK(i) 9.43) to recombinant DOP receptors displaying moderate selectivity over MOP and KOP. In CHO(hDOP) [(35)S]GTPgammaS binding and mouse vas deferens experiments, UFP-502 behaved as a potent (pEC(50) 10.09 and 10.70, respectively) full agonist. In these preparations, naloxone, naltrindole and N,N(CH(3))(2)Dmt-Tic-OH showed similar pA(2) values against UFP-502 and DPDPE and the same rank order of potency. In vivo in mice, UFP-502 mimicked DPDPE actions, producing a significant reduction of immobility time after intracerebroventricular administration in the forced swimming test and a clear antinociceptive effect after intrathecal injection in the tail withdrawal assay. However, while the effects of DPDPE were fully prevented by naltrindole those evoked by UFP-502 were unaffected (tail withdrawal assay) or only partially reversed (forced swimming test). In conclusion, UFP-502 represents a novel and useful chemical template for the design of selective agonists for the DOP receptor.

New 2',6'-dimethyl-L-tyrosine (Dmt) opioid peptidomimetics based on the Aba-Gly scaffold. Development of unique mu-opioid receptor ligands

The Aba-Gly scaffold, incorporated into Dmt-Tic ligands (H-Dmt-Tic-Gly-NH-CH2-Ph, H-Dmt-Tic-Gly-NH-Ph, H-Dmt-Tic-NH-CH2-Bid), exhibited mixed micro/delta or delta opioid receptor activities with micro agonism. Substitution of Tic by Aba-Gly coupled to -NH-CH2-Ph (1), -NH-Ph (2), or -Bid (Bid=1H-benzimidazole-2-yl) (3) shifted affinity (Ki(micro)=0.46, 1.48, and 19.9 nM, respectively), selectivity, and bioactivity to micro-opioid receptors. These compounds represent templates for a new class of lead opioid agonists that are easily synthesized and suitable for therapeutic pain relief.

New series of potent delta-opioid antagonists containing the H-Dmt-Tic-NH-hexyl-NH-R motif

Heterodimeric compounds H-Dmt-Tic-NH-hexyl-NH-R (R=Dmt, Tic, and Phe) exhibited high affinity to delta- (K(i)delta=0.13-0.89nM) and mu-opioid receptors (K(i)mu=0.38-2.81nM) with extraordinary potent delta antagonism (pA(2)=10.2-10.4). These compounds represent the prototype for a new class of structural homologues lacking mu-opioid receptor-associated agonism (IC(50)=1.6-5.8muM) based on the framework of bis-[H-Dmt-NH]-alkyl (Okada, Y.; Tsuda, Y.; Fujita, Y.; Yokoi, T.; Sasaki, Y.; Ambo, A.; Konishi, R.; Nagata, M.; Salvadori, S.; Jinsmaa, Y.; Bryant, S. D.; Lazarus, L. H. J. Med. Chem.2003, 46, 3201), which exhibited both high mu affinity and bioactivity.

Synthesis and opioid activity of N,N-dimethyl-Dmt-Tic-NH-CH(R)-R' analogues: acquisition of potent delta antagonism

N,N-Dimethylation of the H-Dmt-Tic-NH-CH(R)-R' series of compounds produced no significant affect on the high delta-opioid receptor affinity (K(i)=0.035-0.454 nM), but dramatically decreased that for the micro-opioid receptor. The effect of N-methylation was independent of the length of the linker (R); however, the bioactivities were affected by the chemical composition of the third aromatic group (R'): phenyl (Ph) (5'-8') elicited a greater reduction in micro-affinity (40-70-fold) compared to analogues containing 1H-benzimidazole-2-yl (Bid) (9-fold). The major consequences of N,N-dimethylation on in vitro bioactivity were: (i). a loss of delta-agonism coupled with the appearance of potent delta antagonism (4'-7') (pA(2)=8.14-9.47), while 1 exhibited only a 160-fold decreased delta agonism (1') and the delta antagonism of 8 enhanced >10-fold (pA(2)=10.62, 8'); and (ii). a consistent loss of micro-affinity resulted in enhanced delta-opioid receptor selectivity. With the exception of compound 1', the change in the hydrophobic environment at the N-terminus and formation of a tertiary amine by N,N-dimethylation in analogues of the Dmt-Tic pharmacophore produced potent delta-selective antagonists.

Inhibition of human multidrug resistance P-glycoprotein 1 by analogues of a potent δ-opioid antagonist

Analogues Dmt-Tic (2',6'-dimethyl-L-tyrosine-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) pharmacophore, a potent delta-opioid receptor antagonist, inhibited hMDR1 P-GP expressed in a G-185 fibroblast cell line in a manner similar to verapamil. N,N(Me)2-Dmt-Tic-NH-1-adamantane, H-Dmt-Tic-NH-1-adamantane, H-Dmt-Tic-Ala-NH-1-adamantane and N,N(Me)2-Dmt-Tic-NH-tBut were highly effective inhibitors. Weaker inhibition was observed with N,N(Et)2-Dmt-Tic-OH, H-Dmt-Tic-Ala-NH-tert-butyl amide and cyclo(Dmt-Tic). Results demonstrate that N- and C-terminal hydrophobic/lipophilic analogues of the Dmt-Tic pharmacophore inhibit hMDR1 and point to a potential role as chemosensitizing agents in chemotherapy for cancers containing hMDR1.

Synthesis and binding characteristics of [3H] H-Tyr-Ticpsi[CH2-NH] Cha-Phe-OH, a highly specific and stable delta-opioid antagonist

Substitution of the Phe3 aromatic ring in H-Tyr-Ticpsi[CH2-NH]Phe-Phe-OH with cyclohexylalanine (Cha) has been reported to result in a compound, H-Tyr-Ticpsi[CH2-NH]Cha-Phe-OH (TICP[psi]), showing substantially increased delta-opioid antagonist potency and high delta selectivity. TICP[psi] was radiolabeled by catalytic tritiation of its precursor Tyr(3',5'-I2)1TICP[psi]. Binding characteristics of the new tritiated pseudopeptide were determined using the radioligand binding assay in rat brain membranes. On the basis of the results of saturation binding studies performed at 25 degrees C, an equilibrium dissociation constant (Kd) of 0.35 nM and a receptor density (Bmax) of 112 fmol/mg protein were calculated. This new tritiated ligand exhibits high affinity for delta-opioid receptors, whereas its binding to mu and kappa receptors is weak. A study of [H3]TICP[psi] binding displacement by various receptor-selective opioids showed the following rank order of potency: delta > kappa = mu. These receptor binding characteristics of the ligand, together with its high specific radioactivity (41.3 Ci/mmol) and stability, makes it a useful tool for labeling delta-opioid receptors, both in vitro and in vivo.

Activation of diketopiperazine formation by alkylammonium carboxylate salts and aprotic dipolar protophobic solvents

Diketopiperazine formation from the N-terminal residues of a peptide chain is accelerated by aprotic dipolar protophobic solvents and catalyzed in organic solvents by alkylammonium carboxylate salts. The t1/2 for the first-order reaction of H-Ala-Pro-NH2 x TFA falls from 20 d in methanol to 3.6 min in acetonitrile containing 0.02 mol dm(-3) triethylammonium acetate; for H-Ala-Ala-NH2 x TFA in the same reaction media t1/2 falls from an unmeasurably long time to 1.3 d.

Opioid diketopiperazines: synthesis and activity of a prototypic class of opioid antagonists

Discovery of high affinity and ultraselective delta opioid dipeptide antagonists composed of 2',6'-dimethyl-L-tyrosyl (Dmt) and 1,2,3,4-tetrahydroisoquinoline-3-carboxylic (Tic) served as the basis for the conformationally restricted diketopiperazine cyclo(Dmt-Tic) and related open chain analogues. These peptides primarily bind to delta opioid receptors: c(Dmt-Tic) displayed 30- to 50-fold higher delta affinity (Ki delta) than its diastereo-isomeric analogues and more than 4000-fold greater than its Tyr cognate; all of the c(Tyr-Tic) analogues were essentially inactive; c[(N-methyl)Dmt-Tic] lost 5-fold in Ki delta, while Ki mu increased 10-fold to yield a nonselective peptide; and the c(Dmt-Phe) series exhibited considerably reduced binding which indicated a synergism between Dmt and Tic in the binding mechanism. Whereas acetyl-Dmt-Tic linear peptides weakly interacted with opioid receptors, Ac-Dmt-Tic-NH2, exhibited better delta antagonist activity than c(Dmt-Tic) and greater delta receptor selectivity (Ki mu/Ki delta = 570). A three point attachment hypothesis for the interaction between c(Dmt-Tic) and the delta receptor was proposed: hydrophobicity imparted by the aromatic rings and the methyl groups of Dmt, hydrogen bonding through the tyramine hydroxyl group, and cation-pi interactions were suggested as contributing factors in binding the diketopiperazine in the receptor pocket. Although c(Dmt-Tic) exhibited a weak antagonist activity with mouse vas deferens, this diketopiperazine may provide a scaffolding for the formation of more potent antagonists for potential therapeutic applications.