Structure-activity relationships of biphalin analogs and their biological evaluation on opioid receptors.

Biphalin (Tyr-D-Ala-Gly-Phe-NH-NH < -Phe < -Gly < -D-Ala < -Tyr) is an opioid octapeptide with a dimeric structure based on two identical pharmacophore portions, derived from enkephalins, joined "tail to tail" by a hydrazide bridge. This particular structure enhances the antinociceptive activity of the native enkephalins with an unknown mechanism, probably based on a cooperative binding and improved enzymatic stability. Biphalin has excellent binding affinity for µ and δ receptors and it is a highly potent analgesic, as potent as or more than ethorphine. A definitive explanation of the extraordinary in vivo potency shown by this compound, which has pronounced efficacy in pain modulation, is still not available; it has been suggested, however, that the high agonist activity may be related to its binding mode at both µ and δ opioid receptors. Biphalin has significantly higher potency than other analgesics with novel biological profiles; in particular, most recent data show that biphalin is unlikely to produce dependency in chronic use. In the past 20 years, there have been many attempts to modify its structure to obtain products unaffected by the action of enkephalinases, to enhance its antinociceptive activity and to modify the BBB penetration. In addition, structure-activity relationship studies (SAR) were performed in order to understand the elements responsible for biphalin's high activity. The aim of the studies reported in this review was to clarify: i) the role of the hydrazide bridge, ii) the role of residues in position 4, 4' and 3, 3', iii) the consequences of molecular simplifications (truncation, delection), iv) the consequences of cyclization through a disulfide bridge, v) conjugation with PEG and fluorescet residues, and vi) radiolabeling on Tyr.

(Acyloxy)alkoxy moiety as amino acids protecting group for the synthesis of (R,R)-2,7 diaminosuberic acid via RCM.

A new synthetic pathway is described to prepare asymmetrically protected 2,7-diaminosuberic acid. This strategy exploits (acyloxy)alkoxy promoiety as protecting group and RCM reaction using second generation Grubbs catalyst and provides the trans isomer of (2R,7R)-7-(((9H-fluoren-9-yl)methoxy)carbonylamino)-2-(tert-butoxycarbonylamino)-8- methoxy-8-oxooct-4-enoic acid, which was in turn reduced to obtain (2R,7R)-7-(((9H-fluoren-9-yl)methoxy)carbonylamino)- 2-(tert-butoxycarbonylamino)-8-methoxy-8-oxooctanoic acid.

Synthesis and biological evaluation of new active For-Met-Leu-Phe-OMe analogues containing para-substituted Phe residues.

In the present study, we report synthesis and biological evaluation of the N-Boc-protected tripeptides 4a-l and N-For protected tripeptides 5a-l as new For-Met-Leu-Phe-OMe (fMLF-OMe) analogues. All the new ligands are characterized by the C-terminal Phe residue variously substituted at position 4 of the aromatic ring. The agonism of 5a-l and the antagonism of 4a-l (chemotaxis, superoxide anion production, lysozyme release as well as receptor binding affinity) have been examined on human neutrophils. No synthesized compounds has higher activity than the standard fMLF-OMe tripeptide to stimulate chemotaxis, although compounds 5a and 5c with -CH(3) and -C(CH(3))(3), respectively, in position 4 on the aromatic ring, are better than the standard tripeptide to stimulate the production of superoxide anion, in higher concentration. Compounds 4f and 4i, containing -F and -I in position 4, respectively, on the aromatic ring of phenylalanine, exhibit significant chemotactic antagonism. The influence of the different substitution at the position 4 on the aromatic ring of phenylalanine is discussed.

The cis-4-amino-L-proline residue as a scaffold for the synthesis of cyclic and linear endomorphin-2 analogues.

Endomorphin-2 (EM-2: Tyr-Pro-Phe-Phe-NH(2)) is an endogenous tetrapeptide that combines potency and efficacy with high affinity and selectivity toward the µ opioid receptor, the most responsible for analgesic effects in the central nervous system. The presence of the Pro(2) represents a crucial factor for the ligand structural and conformational properties. Proline is in fact an efficient stereochemical spacer, capable of inducing favorable spatial orientation of aromatic rings, a key factor for ligand recognition and interaction with receptors. Here the Pro(2) has been replaced by 4(S)-NH(2)-2(S)-proline (cAmp), a proline/GABA cis-chimera residue. This bivalent amino acid maintains the capacity to influenc the tetrapeptide conformation and offers the opportunity to generate new linear models and unusually constrained cyclic analogues characterized by an N-terminal Tyr bearing a free α-amino group. The results indicate that the new analogues do not show affinity for both δ and κ opioid receptors and bind only poorly to the µ receptors (for cyclopeptide 9: K(i)(µ) = 660 nM; GPI (IC(50)) = 1.4% at 1 µM; for linear tetrapeptide acid 13: K(i)(µ) = 2000 nM; GPI (IC(50)) = 0% at 1 µM; for linear tetrapeptide amide 15: K(i)(µ) = 310 nM; GPI (IC(50)) = 894 nM).

Delivery methods of camptothecin and its hydrosoluble analogue irinotecan for treatment of colorectal cancer.

Camptothecins are a family of alkaloids originally extracted from the Chinese tree Camptotheca acuminata, Nyssaceae, exhibiting a strong activity against colorectal cancer (CRC). CRC is a common malignancy worlwide. Despite significant developments in the treatment of this disease, it still causes considerable morbidity and mortality. Recent advances include both newer cytotoxic chemotherapies and novel biological agents including the more hydrosoluble camptothecin derivative, namely irinotecan. Camptothecin and irinotecan are selective human topoisomerase I inhibitors but their application for curing CRC is compromised by their intrinsic high toxicity, insolubility and instability. Furthermore, pharmacology studies have determined that continuously and prolonged schedules of administration are required. The aim of this work is to review the state of the art of camptothecin and its derivative irinotecan's delivery methods.

Conformationally constrained histidines in the design of peptidomimetics: strategies for the χ-space control.

A successful design of peptidomimetics must come to terms with χ-space control. The incorporation of χ-space constrained amino acids into bioactive peptides renders the χ(1) and χ(2) torsional angles of pharmacophore amino acids critical for activity and selectivity as with other relevant structural features of the template. This review describes histidine analogues characterized by replacement of native α and/or ß-hydrogen atoms with alkyl substituents as well as analogues with α, ß-didehydro unsaturation or C(α)-C(ß) cyclopropane insertion (ACC derivatives). Attention is also dedicated to the relevant field of ß-aminoacid chemistry by describing the synthesis of ß(2)- and ß(3)-models (ß-hHis). Structural modifications leading to cyclic imino derivatives such as spinacine, aza-histidine and analogues with shortening or elongation of the native side chain (nor-histidine and homo-histidine, respectively) are also described. Examples of the use of the described analogues to replace native histidine in bioactive peptides are also given.

New potent biphalin analogues containing p-fluoro-L-phenylalanine at the 4,4' positions and non-hydrazine linkers.

We report the synthesis and the biological evaluation of two new analogues of the potent dimeric opioid peptide biphalin. The performed modification is based on the replacement of two key structural elements of the native biphalin, namely: the hydrazine bridge which joins the two palindromic moieties and the phenylalanine residues at the 4,4' positions of the backbone. The new analogues 9 and 10 contain 1,2-phenylenediamine and piperazine, respectively, in place of the hydrazidic linker and p-fluoro-L-phenylalanine residues at 4 and 4' positions. Binding values are: Kµ(i)=0.51 nM and Kδ(i)=12.8 nM for compound 9, Kµ(i)=0.09 nM and Kδ(i)=0.11 nM for analogue 10.

Synthesis and activity of endomorphin-2 and morphiceptin analogues with proline surrogates in position 2.

The opioid agonists endomorphins (Tyr-Pro-Trp-Phe-NH(2); EM1 and Tyr-Pro-Phe-Phe-NH(2); EM2) and morphiceptin (Tyr-Pro-Phe-Pro-NH(2)) exhibit an extremely high selectivity for mu-opioid receptor. Here a series of novel EM2 and morphiceptin analogues containing in place of the proline at position 2 the S and R residues of beta-homologues of proline (HPro), of 2-pyrrolidinemethanesulphonic acid (HPrs) and of 3-pyrrolidinesulphonic acid (betaPrs) have been synthesized and their binding affinity and functional activity have been investigated. The highest micro-receptor affinity is shown by [(S)betaPrs(2)]EM2 analogue (6e) which represents the first example of a beta-sulphonamido analogue in the field of opioid peptides.

Synthesis and evaluation of new endomorphin-2 analogues containing (Z)-alpha,beta-didehydrophenylalanine (Delta(Z)Phe) residues.

New endomorphin-2 (EM-2) analogues incorporating (Z)-alpha,beta-didehydrophenylalanine (Delta(Z)Phe) in place of the native phenylalanine in EM-2 are reported. Tyr-Pro-Delta(Z)Phe-Phe-NH(2) {[Delta(Z)Phe(3)]EM-2} (1), Tyr-Pro-Phe-Delta(Z)Phe-NH(2) {[Delta(Z)Phe(4)]EM-2} (2), and Tyr-Pro-Delta(Z)Phe-Delta(Z)Phe-NH(2) {[Delta(Z)Phe(3,4)]EM-2}(3) have been synthesized, their opioid receptor binding affinities and tissue bioassay activities were determined, and their conformational properties were examined. Compound 2 shows high mu opioid receptor selectivity and mu agonist activity comparable to those of the native peptide. The conformation adopted in solution and in the crystal by N-Boc-Tyr-Pro-Delta(Z)Phe-Phe-NH(2) (8) is reported.

N-(tert)-butyloxycarbonyl)-beta,beta-cyclopentyl-cysteine (acetamidomethyl)-methyl ester for synthesis of novel peptidomimetic derivatives.

It has been recently reported that thiol groups could play an important role in the protection of neuronal cells in Alzheimer's disease (AD), prion disease (CJD) and Parkinson's disease (PD). Also bucillamine, that is a pseudo dipeptide possessing a thiol group capable to form an internal disulfide bridge, has relevant scavenger properties used in therapy for the treatment of arthritis. Furthermore, many sulphur containing compounds show strong chelating properties to heavy metals. Due to the crucial role of thiol groups in a variety of detoxicant biological systems, we report the synthesis of a racemic beta,beta-dialkyl-substituted, fully protected, cysteine derivative as a suitable intermediate in the synthesis of novel biological active peptides.

Synthesis and evaluation of new endomorphin analogues modified at the Pro(2) residue.

Six new endomorphin analogues, incorporating constrained amino acids in place of native proline have been synthesized. Residues of (S)-azetidine-2-carboxylic acid (Aze), 3,4-dehydro-(S)-proline (Delta(3)Pro), azetidine-3-carboxylic acid (3Aze) and dehydro-alanine (DeltaAla) have been used to prepare [Delta(3)Pro(2)]EM-2 (1), [Aze(2)]EM-1 (2), [Aze(2)]EM-2 (3), [3Aze(2)]EM-1 (4), [3Aze(2)]EM-2 (5) and [DeltaAla(2)]EM-2 (6). Binding assays and functional bioactivities for mu- and delta-receptors are reported. The highest affinity, bioactivity and selectivity are shown by peptides 2 and 3 containing the Aze residue.

Novel chemotactic For-Met-Leu-Phe-OMe (fMLF-OMe) analogues based on met residue replacement by 4-amino-proline scaffold: synthesis and bioactivity.

cis-(2S,4S) 4-amino-proline (cAmp) and trans-(2S,4R) 4-amino-proline (tAmp) residues, bearing N-For or N-Boc substituents at the two amino groups, have been incorporated into the potent chemotactic agent fMLF-OMe in place of the N-terminal native (S)-methionine to give the analogues 17a-19a and 17b-19b. The new ligands have been examined for their activity (chemotaxis, superoxide anion production and lysozyme release) on human neutrophils as agonists and antagonists. Compounds 19a and 19b, bearing two N-For groups at the proline scaffold, are active and selective chemoattractants. The ligand 18b, containing N-For at the 4-amino group of the N-Boc-tAmp residue, exhibits significant chemotactic antagonism. The influence of the different substitution at the N-terminal position of the new analogues is discussed.