Structure activity of C-terminal modified analogs of Ac-CCK-7.

Previous work indicates that both the C-terminal phenylalanine amide and the tryptophan moieties of cholecystokinin (CCK) are critical pharmacophores for interaction with either the A or B receptor subtypes. We have examined a series of analogs of Ac-CCK-7 [Ac-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe33-NH2] (2) in which the phenyl ring of the C-terminal Phe-NH2 has been modified. Compounds were assessed in binding assays using homogenated rat pancreatic membranes and bovine striatum as the source of CCK-A and CCK-B receptors respectively and for anorectic activity after intraperitoneal administration to rats. Substitution of a number of cycloalkyl or bicyclic aryl moieties for the phenyl ring of phenylalanine33 including cyclopentyl (20), cyclohexyl (21), cyclooctyl (23), 2-(5,6,7,8-tetrahydro)naphthyl (26), 2-naphthyl (27), and 1-naphthyl (29) led to analogs with 10-70 times the anorectic potency of 2. The anorectic activity of 21 was blocked by the specific CCK-A receptor antagonist MK-329. Other bulky aliphatic groups in place of the phenylalanine33 aromatic ring such as isopropyl, 2-adamantyl and cyclohexylmethyl gave derivatives similar to 2 in potency. While most of the new compounds were comparable to CCK in binding assays, 23, 26, 27 and 29 were exceptionally potent with IC50s 10(-11)-10(-14) M in the pancreas. Compounds 23 and 29 were further evaluated for their ability to stimulate amylase secretion and found to have potencies similar to that of CCK. The dissociation between potency in the binding and amylase secretion assays suggests that they may interact with a high affinity binding site which is not coupled to amylase secretion. We conclude that CCK receptors possess a generous hydrophobic pocket capable of accommodating large alkyl groups in place of the side chain of phenylalanine33 and that the pharmacological profile of CCK analogs can be tailored by appropriate exploitation of this finding.     

Vasopressin antagonist analogs modified at position 7

Vasopressin antagonist analogs having alanine or glycine at position 7 were essentially equipotent with analogs with proline, N-methylalanine or sarcosine at position 7. This demonstrates that the conformational constraint imposed by an N-alkyl residue at position 7 is not necessary for binding of antagonist to the receptor, the exact opposite of what is seen in agonists. This suggests that antagonists bind to the receptor in a manner which is very different from that of agonists.     

Interaction between tryptophanyl-tRNA synthetase and tryptophan analogs with modified alpha-amino group

Analogs of L-tryptophane with modified alpha-amino groups (substituted for hydrogen or keto-group, or acylated) are competitive reversible inhibitors of the aminoacylation of tRNNATrp catalyzed by tryptophanyl-tRNA synthetase from beef pancreas. Compounds lacking alpha-amino group are weakly bound to the enzyme, whereas the Ki values for N-acylated L-tryptophane derivates and for beta-indolylpyruvic acid are similar and approximately two orders of magnitude higher than the KM value for L-tryptophane.     

Synthesis of cytotoxic novel 9,11-secosterol analogs: Structure/activity studies

In an effort to determine the pharmaceutical utility and the structural requirements for activity against tumor cell lines, 30 novel 9,11-secosterol analogues with different side chains and degrees of oxidation at C-9 were synthesized starting from hecogenin. Evaluation of the synthesized compounds for cytotoxicity against KB, HeLa and MCF-7 cell lines revealed that some important structural features are required for activity. The presence of a cholesterol-type side chain, which appears to play a major role in determining the biological activity, the existence of a ketone functional at C-9 is also crucial for anticancer activity whereas hydroxyl/ketone function at C-22 on the side chain did not increase cytotoxicity.     

Synthesis and biophysical studies of modified oligonucleotides containing acyclic amino alcohol nucleoside analogs.

Novel serine derivative of thymine was prepared and incorporated into oligonucleotides. These modified oligonucleotides were studied for their binding affinity with complementary DNA/RNA.     

Structure and binding properties of hen lysozyme modified at tryptophan 62

The structure of a derivative of hen egg-white lysozyme (EC 3.2.1.17) modified by N-bromosuccinimide at Trp62 has been studied by both ¹H nuclear magnetic resonance spectroscopy and X-ray crystallography. It was shown that this modification, changing the tryptophan residue to an oxindolealanine² residue, only causes minor structural changes at the site of the modification, and that the overall structure of the native enzyme is maintained in the derivative. Both diastereomers of the oxindolealanine-62 lysozyme were observed by the two methods employed, in accordance with previous observations (Norton & Allerhand, 1976). The pK values of the catalytically important carboxyl groups of Glu35 and Asp52 were identical in the native enzyme and its derivative. However, the modified enzyme is virtually inactive in the hydrolysis of the cell-wall mucopolysaccharide of Micrococcus lysodeikticus. The binding of N-acetylglucosamine oligosaccharides to both native lysozyme and Ox-62 lysozyme was studied by nuclear magnetic resonance spectroscopy, observing the perturbations on the lysozyme ¹H n.m.r. resonances, and differences in the perturbations of the two systems demonstrated that binding of (GlcNAc)₃ in particular was not identical in the two systems. The structure of Ox-62 lysozyme-(GlcNAc)₃ was studied by X-ray crystallography and it was shown that only two GlcNAc residues make contact with the enzyme, binding the reducing end residue in a similar mode as the α-anomeric form of GlcNAc binds to the native enzyme (Blake et al., 1967a). On the basis of the results obtained by X-ray crystallography and ¹H n.m.r. spectroscopy, the lack of enzymatic activity of the Ox-62 lysozyme arises from the obstruction by the oxindolealanine residue of sub-site B of the active site, preventing productive binding of the substrate.     

Partitioning of tryptophan side-chain analogs between water and cyclohexane.

We have measured the partitioning of the tryptophan side-chain analogs 3-methylindole and N-methylindole between water and cyclohexane over the temperature range 8-55 degrees C to investigate the relative contribution of the imine-NH- to the free energy of transfer. We take advantage of the fact that the indole imine nitrogen is blocked by a methyl group in N-methylindole. Unlike previous studies, we take into account the water present in the cyclohexane phase. Free energies of partitioning were calculated using mole-fraction, volume-fraction, and Flory-Huggins-corrected volume-fraction partition coefficients [De Young, L. R., & Dill, K. A. (1990) J. Phys. Chem. 94, 801-809; Sharp, K. A., Nicholls, A., Friedman, R., & Honig, B. (1991) Biochemistry 30, 9686-9697]. These approaches account for configurational entropy changes in different ways and thus lead to different values for the calculated free energies of transfer. There is a 2-3-fold difference in the free energies calculated from our measurements, using the different units. Independent of units, the partitioning of both compounds involves identical entropy changes. However, 3-methylindole has an additional unfavorable enthalpic contribution to partitioning into cyclohexane of +1.6 kcal/mol (independent of units) which is presumably the cost of removing the indole -NH- group from water and transferring it to cyclohexane. In cyclohexane, 3-methylindole forms hydrogen bonds with water that cause water to copartition into cyclohexane with the solute. A method is described which allows the partitioning process to be examined independent of subsequent interactions with water in the solvent.     

Structure activity studies of the melanocortin antagonist SHU9119 modified at the 6, 7, 8, and 9 positions

The melanocortin system is involved in the regulation of several diverse physiological pathways, including energy homeostasis. Several synthetic peptide analogs have been designed, synthesized, and pharmacologically characterized at the mouse melanocortin receptor subtypes MC1R, MC3R, MC4R, and MC5R. These peptides incorporate modifications of the melanocortin core amino acids His-Phe-Arg-Trp by using the cyclic lactam templates of the lead structures MTII and SHU9119. Analogs containing DNal(2') at position 7 resulted in partial agonist and antagonistic activities at the mMC3R while possessing full antagonistic activities at the mMC4R. Recently, the melanocortin-5 receptor (MC5R) has been demonstrated to have a role in the regulation of exocrine gland function. This study has characterized the following analogs of SHU9119 that possess antagonist activity at the MC5R: Ac-Nle-c[Asp-(1-Me)His(6)-DNal(2')(7)-Arg-Trp-Lys]-NH(2), pA(2) = 7. 1; Ac-Nle-c[Asp-(1-Me)His(6)-DNal(2')(7)-Arg-Nal(2')(9)-Lys]-NH(2), pA(2) = 7.2; and Ac-Nle-c[Asp-Trp(6)-DNal(2')(7)-Arg-Nal(2')(9)-Lys]-NH(2), pA(2) = 6. 6.     

Synthesis, activity on NK-3 tachykinin receptor and conformational solution studies of scyliorhinin II analogs modified at position 16.

Two analogs of a tachykinin family peptides - scyliorhinin II (ScyII): [Aib(16)]ScyII and [Sar(16)]ScyII were synthesized by the solid-phase method using Fmoc chemistry. Conformational studies in water and DMSO-d(6) on these peptides were performed using a combination of two-dimensional NMR and theoretical conformational analysis. The solution structure of the peptides studied is interpreted as an equilibrium of several conformers with different statistical weights. The structure of [Sar(16)]ScyII in water appeared to be more flexible, especially in the C-terminal fragment. A better defined structure for this analog was obtained in DMSO-d(6), in which the analysis resulted in a family of conformers with similar shapes. Some of these conformers were characterized by the presence of a 3(10)-helix in the N-terminal fragment and middle part of the molecule. The introduction of the Aib residue in position 16 significantly rigidifies the structure. For [Aib(16)]ScyII in both solvent systems very similar populations of conformations were obtained which are characterized by the presence of a 3(10)-helix in the 13-18 fragment. A common structural motif was found in conformationally constrained Cys(7)-Cys(13) fragment, which resembles the Greek letter 'omega'. The differences in the solution structure of the C-terminal fragment of the peptides studied are responsible for their specificity. [Aib(16)]ScyII showed 25% the agonistic activity of selective NK-3 agonist - senktide, but it also showed antagonist effect vs. this peptide, whereas [Sar(16)]ScyII appeared to be a full agonist of NK-3 tachykinin receptor.     

Biological activity of cholecystokinin-(30-33) tetrapeptide analogs

Analogues of the endogenous peptide corresponding to the 30-33 sequence of cholecystokinin (Trp-Met-Asp-Phe-NH2) were synthesized, and their biological activity was studied. It was shown that, in rats, the N-succinylated Nle2 analogue of this tetrapeptide exhibits increased anxiolytic properties in the dark-bright chamber test and an enhanced alcohol intake by both the control animals and the long-time alcohol-dependent animals under the conditions of free choice. Introduction of an isopropyl residue into the C-terminal amide of the Nle2 analogue resulted in the appearance of anxiolytic and antialcohol activity and the ability to increase the morphine analgesic effect in the tail-flick test on rats. The two synthesized analogues retained an affinity to cholecystokinin receptors.     

Structure activity relationship studies with hypothalamic peptide hormones. II. Effects of thyrotropin releasing hormone analogs on morphine-induced responses in mice

The effects of several analogs of thyroliberin (TRH), that have a chloro-acetyl substituent at the amino terminus, on locomotor depressant, locomotor stimulant, hyperthermic and hypothermic response to morphine were determined in the mouse. These compounds included N-(chloroacetyl)-L-phenylalanylpyrrolidine (ClAc-Phe-Pyrr), N-[m-(chloroacetyl)benzoyl]-L-phenylalanylpyrrolidine] (mClAcBz-Phe-Pyrr), N-[m-(chloroacetyl)benzoyl]-L-alanyl-L-phenylalanylpyrrolidine (mClAcBz-Ala-Phe-Pyrr), N-[p-(chloroacetyl)benzoyl]-L-alanyl-L-phenylalanyl-pyrrolidine (pClAcBz-Ala-Phe-Pyrr), N-(chloroacytyl)-L-alanyl-L-phenylalanyl-L-prolineamide(ClAc-Ala-Phe-Pro-NH₂), N-[m-(chloroacetyl)-benzoyl]-L-phenylalanyl-L-prolineamide (mClAcBz-Phe-Pro-NH₂), N-[p-(chloroacetyl)benzoyl]-L-phenylalanyl-L-prolineamide (pClAcBz-Phe-Pro-NH₂). Since TRH is metabolized to cyclo (His-Pro) and the latter is shown to possess TRH like activity, an analog cyclo (Phe-Pro) was also used. Administration of morphine to mice at 10 mg/kg ip produced hyperthermia and depression in locomotor activity, while at 80 mg/kg ip, hypothermia and stimulation in locomotor activity were observed. Intracerebral injection of the following peptides (10 μg each per mouse) administered 10 min prior to morphine injection antagonized locomotor depression, hyperthermia, locomotor stimulation and hypothermia induced by an appropriate dose of morphine: mClAcBz-Phe-Pyrr, pClAcBz-Ala-Phe-Pyrr, ClAcAla-Phe-Pro-NH₂, pClAcBz-Phe-Pro-NH₂, cyclo (Phe-Pro) and TRH. The compounds which had no effect on low dose or high dose morphine induced responses included pGlu-Phe-Pyrr, mClAcBz-Ala-Phe-Pyrr, and mClAcBz-Phe-Pro-NH₂. One compound, namely ClAc-Phe-Pyrr, antagonized morphine-induced locomotor stimulation and hypothermia but did not affect locomotor depression and hyperthermia produced by morphine. None of these peptides had any effect on the body temperature or the locomotor activity of normal mice. Many of the active compounds were previously shown to possess extremely weak or no activity in releasing thyrotropin from the pituitary. It is concluded that several of these analogs of TRH possess CNS activity in antagonizing morphine effects, and that a lack of relationship exists between the CNS and endocrine activity of these peptides.     

Synthesis and activity of partial retro-inverso modified atrial natriuretic factor analogs

The synthesis and pharmacological activity of partial retro-inverso modified rat atrial natriuretic factor (rANF) analogs is described. The route to these compounds utilized a combination of solution and solid-phase methods. The analogs prepared all contain a reversed amide bond (psi[NHCO]) at the Ser 25 to Phe26 linkage. This bond has been suggested to play a key role in the metabolic inactivation of ANF. The analogs are of comparable potency to the endogenous peptide rANF1-28 in binding to cultured rat vascular smooth muscle cells, in relaxing serotonin contracted rabbit aortic rings, and as natriuretic/diuretic agents in anesthetized rats. None of the peptides has an extended duration of action in vivo.     

Effect of tryptophan analogs on derepression of the Escherichia coli tryptophan operon by indole-3-propionic acid.

The abilities of 14 tryptophan analogs to repress the tryptophan (trp) operon have been studied in Escherichia coli cells derepressed by incubation with 0.25 mM indole-3-propionic acid (IPA). trp operon expression was monitored by measuring the specific activities of anthranilate synthase (EC 4.1.3.27) and the tryptophan synthase (EC 4.2.1.20) beta subunit. Analogs characterized by modification or removal of the alpha-amino group or the alpha-carboxyl group did not repress the trp operon. The only analogs among this group that appeared to interact with the trp aporepressor were IPA, which derepressed the trp operon, and d-tryptophan. Analogs with modifications of the indole ring repressed the trp operon to various degrees. 7-Methyl-tryptophan inhibited anthranilate synthase activity and consequently derepressed the trp operon. Additionally, 7-methyltryptophan prevented IPA-mediated derepression but, unlike tryptophan, did so in a non-coordinate manner, with the later enzymes of the operon being relatively more repressed than the early enzymes. The effect of 7-methyltryptophan on IPA-mediated derepression was likely not due to the interaction of IPA with the allosteric site of anthranilate synthase, even though feedback-resistant mutants of anthranilate synthase were partially resistant to derepression by IPA. The effect of 7-methyltryptophan on derepression by IPA was probably due to the effect of the analog-aporepressor complex on trp operon expression.     

Inhibition of rat liver tryptophan pyrrolase activity and elevation of brain tryptophan concentration by administration of DL-alpha-amino-beta-pyridinepropanoic acid (pyridylalanine) analogs

Single doses of DL-alpha-amino-beta-(2-pyridine)propanoic acid (2-PA, 100 mg/kg) significantly decreased the holoenzyme and apoenzyme activities of rat liver tryptophan pyrrolase (TP) and increased brain tryptophan, serotonin (5-HT) and 5-hydroxyindole-3-ylacetic acid concentrations. 2-PA had no inhibitory effect on either of the enzyme activities in vitro, but its expected metabolites were effective. Single doses of DL-alpha-amino-beta-(3-pyridine)propanoic acid (3-PA, 100 mg/kg) decreased only the holoenzyme activity and elevated brain tryptophan and its metabolites levels in rats. 3-PA and its metabolite, 3-pyridylpyruvate, inhibited only the holoenzyme activity in vitro. DL-alpha-Amino-beta-(4-pyridine)propanoic acid (4-PA) caused significant changes in liver TP (holo- and apoenzyme forms) activity and brain tryptophan concentration only after repeated administration (100 mg/kg/day). 4-PA was a weak inhibitor of the holoenzyme, but its metabolites apparently inhibited the holo- and apoenzyme activities in vitro. These findings suggest that PA analogs (and/or their metabolites) increased brain tryptophan (and hence 5-HT synthesis) by directly inhibiting liver TP activity.     

Selection of cell lines resistant to tryptophan analogs

After prolonged cultivation in the presence of increasing amounts of carboxyl-substituted tryptophan analogs (tryptamine and tryptophanol), cell lines resistant to high concentrations of these compounds were obtained. The initial culture was the Madin-Darby line of spontaneously transformed bovine kidney cells. In the resistant lines the amount of tryptophanyl-tRNA synthetase (E. C. 6.1.1.2) is manyfold increased as shown by two criteria: (i) enzymatic activity (ATP-PPi isotopic exchange) per mg of protein, (ii) binding of in vivo 35S-labeled proteins to polyclonal antibodies against tryptophanyl-tRNA synthetase. It was shown that tryptophanyl-tRNA synthetase is phosphorylated in vivo, and the degree of phosphorylation of the enzyme in initial cells seems to be higher then in the resistant ones. The Km value for tryptophan is not significantly changed for the enzyme from resistant cells. The permeability for tryptophan and its analogs is reduced in the resistant cells. It is proposed that the acquisition of the resistance against tryptophan analogs are due to alterations at the genomic level (for example, gene amplification etc.).     

Structure–activity studies on seco-pancratistatin analogs: Potent inhibitors of human cytochrome P450 3A4

Two total syntheses of fully functionalized seco-analogs of the anticancer compound pancratistatin are reported. Structure–activity relationship (SAR) studies identified potent and selective inhibitors of human cytochrome P450 3A4 (CYP3A4) and revealed several core pharmacophoric elements. These studies identify potential roadblocks and will guide the further development of a viable selective clinical pancratistatin derivative.     

N-terminal modified analogs of HVFLRFamide with inhibitory activity on the locust oviduct

New N-terminal analogs of the peptide HVFLRFamide, the minimum sequence of the insect myosuppressins capable of inhibiting spontaneous and induced contractions of the locust oviduct, were synthesized and tested for biologic activity on locust oviduct. Most active, as judged by the ability to inhibit proctolin-induced contractions of locust oviduct, was (N(alpha)-acetyl)-HVFLRFamide. D-Pro-HVFLRFamide was also highly inhibitory. Interestingly, low doses of the pentapeptide analog (N(alpha)-imidazoleacrylyl)-VFLRFamide inhibited oviduct contractions. This is the first pentapeptide analog shown to inhibit contractions of locust oviduct, and this result indicates that the alpha-amino group of His is not absolutely required for inhibitory activity. In all cases when His was replaced by a D-amino acid, the analogs were stimulatory, resulting in an increase in basal tonus of the locust oviduct. The results provide further insight into the structural features of the HVFLRFamide molecule that are required for inhibitory activity on locust oviduct muscle.     

Design,synthesis and aphicidal activity of N-terminal modified insect kinin analogs

The insect kinins are a class of multifunctional insect neuropeptides present in a diverse variety of insects. Insect kinin analogs showed multiple bioactivities, especially, the aphicidal activity. To find a biostable and bioactive insecticide candidate with simplified structure, a series of N-terminal modified insect kinin analogs was designed and synthesized based on the lead compound [Aib]-Phe-Phe-[Aib]-Trp-Gly-NH₂. Their aphicidal activity against the soybean aphid Aphis glycines was evaluated. The results showed that all the analogs maintained the aphicidal activity. In particular, the aphicidal activity of the pentapeptide analog X Phe-Phe-[Aib]-Trp-Gly-NH₂ (LC₅₀ = 0.045 mmol/L) was similar to the lead compound (LC₅₀ = 0.048 mmol/L). This indicated that the N-terminal protective group may not play an important role in the activity and the analogs structure could be simplified to pentapeptide analogs while retaining good aphicidal activity. The core pentapeptide analog X can be used as the lead compound for further chemical modifications to discover potential insecticides.