CONH Groups Research Articles

Preparation and characterization of functional group gradient surfaces

AbstractFunctional group gradient surfaces where the density of functional groups changes gradually along the sample length were prepared. The functional group ( COOH,  CONH2, and  OH group) gradient surfaces were produced by the treatment of low‐density PE sheets using a corona with gradually increasing power, followed by the graft copolymerization of acrylic acid and subsequent substitution reaction of carboxylic acid groups to amide or hydroxyl groups. The prepared gradient surfaces were characterized by the measurement of water contact angle, FTIR‐ATR, and ESCA. The gradient surfaces prepared can be used to systematically investigate the interactions of biological or other species in terms of the surface functional groups and their density of polymeric materials. © 1994 John Wiley & Sons, Inc.

Synthesis and inhibitory activity on platelet aggregation of 13'-aza and other omega-chain modified BW245C analogues.

BW245C analogues which have 15'-keto, -oximino, -sulphinyl, -sulphonyl, -methyl, -1-adamantyl, 14'-hydroxy, 16'-hydroxy, 13'-14'-NH=CH, -NH-CH2, or -NH-CO groups have been synthesized and evaluated for their activity in inhibiting platelet aggregation and for their cardiovascular actions: the 13'-aza analogues 13 and 14 are more potent inhibitors of human platelet aggregation than BW245C (0.3, 0.6 and 0.2 x PGI2, respectively) and these inhibitory activities on platelet aggregation increase on incubation in vitro. The prostaglandin mimetic properties of 13 (BW68C) and 14 (BW361C) were studied in more detail and their platelet inhibitory and vasodilatory effects found to be of longer duration than those of BW245C. All other modifications to the omega-chain of BW245C led to less potent or inactive compounds.

Novel Nematogens Derived from N,N′-Dialkanoyl-4-alkanoyloxy-1,3-benzenediamines

Abstract The mesomorphic properties of homologous series of N,N′-dialkanoyl-2,5-dimethyl-4-alkanoyloxy-1,3-benzenediamines and their 2-methyl-5-isopropyl and 2-methyl-5-t-butyl analogues have been studied. All the mesophases appearing in the nonanoyl to hexadecanoyl derivatives of the first series are metastable and nematic in type. By the replacement of the methyl group at the 5-position with an isopropyl or t-butyl group, nematic thermal stability is promoted. As a result, the nonanoyl to tetradecanoyl derivatives in the second series can exhibit a nematic phase with a temperature range of stable existence over 7 to 22°C. The 2-methyl-5-isopropyl compounds, in which the ester alkyl group is different from the other alkyl groups, were also synthesized. The broadest temperature range of stable existence of a nematic phase of 31°C is achieved when tridecyl groups are connected through the CONH groups and a octyl group through the COO group. The t-butyl group at the 5-position stabilizes not only the mesophase but also the crystalline phase; therefore, a nematic phase is detectable only for the undecanoyl to hexadecanoyl derivatives.

Organic Reactions Catalyzed by Modified Enzymes Part II. Application of QSAR methodology to the study of the chemoselectivity of modified α-chymotrypsin in the synthesis of peptides

Quantitative Structure Activity Relationship and Molecular Mechanics methodologies have been applied to the study of the kinetically controlled synthesis of peptides catalyzed by chemically modified α-chymotrypsin (α-CT-PEG), in order to investigateI) the structural properties of the substrate and their effect on the enzymatic activity.II) the dimensions of the active site.The chemical modification of α-CT does not alter the relative position of “ar”, “am” and “h” subsites of α-CT (Figure 1) because only L-aminoacids are accepted as acyl donors. Using the modified enzyme the active conformation of the acyl donor that interacts with the “am”, “ar” and “h” subsites of the modified enzyme is described. The relative position of Ser-195 and the residues that interact with the substrate in the “am” subsite have also been determined. The CO-NH group (interaction with “am” subsite) and the COOCH3 group (interaction with Ser-195) are opposite to each other (−177° to 170°) when bound in the active site. The “ar” and “am” subsites are located with a dihedric angle of − 104° as can be deduced from the relative position of the two aromatic rings of the analogues of N-benzoyl-phenylalanine methyl ester in the active conformer. The dimensions of the “ar” subsite of the modified enzyme are described for the first time. It presents two cavities in front of the ortho and meta positions, with dimensions equivalent to those of a CH3 or Br group.

A New Helicopodand: Molecular Recognition of Dicarboxylic Acids with High Diastereoselectivity

AbstractThe helicopodand (PM)‐2 is prepared following the photocyclodehydrogenation route to helicenes (Scheme). At the ends of a [7]helicene backbone, this acyclic receptor (‘podand’) possesses a H‐bonding recognition site shaped by two convergent N‐(pyridin‐2‐yl)carboxamide (CONH(py)) units. In the crystal of diethyl [7]helicene‐2,17‐dicarboxylate ((PM)‐3), a direct synthetic precursor of 2, molecules of the same chirality form stacks, and two stacks of opposite chirality are interlocked in a pair having average face‐to‐face aromatic contacts of 3.82 Å between benzene rings of different enantiomers (Fig. 2). In contrast, two conformations are observed in the crystal structure of 2, one with both CONH(py) residues pointing with their H‐bonding centers NH/N away from the binding site (‘out‐out’) and a second (‘in‐out’) with one of the two CONH(py) residues pointing towards the binding site (‘in’; Fig. 4). While no H‐bonding network propagates throughout the crystal, enantiomers of 2 in the different conformations ‘out‐out’ and ‘in‐out’ form H‐bonded pairs that are further stabilized by a H‐bond to one molecule of CHCl3. In the productive ‘in‐in’ conformation, 2 forms stable 1:1 complexes with α,ω‐dicarboxylic acids in CHCl3, and a diastereoselectivity in complexation of Δ(ΔG°) = 1.4 kcal mol−1 is measured for two substrates differing only in the (E)/(Z)‐configuration at their double bond (see Table 2). A comprehensive force‐field molecular‐modeling study suggests that only the (E)‐derivative possesses the correct geometry for a ditopic four‐fold H‐bonding interaction between its two COOH residues and the two CONH(py) groups in 2 (Fig. 5). With N,N′‐bis [(benzyloxy)carbonyl]‐L‐cystine, the formation of diastereoisomeric complexes with (PM)‐2 is observed (Fig. 7).

Peptide mimics for structural features in proteins

The crystal structure determination of three heptapeptides containing alpha-aminoisobutyryl (Aib) residues as a means of helix stabilization provides a high-resolution characterization of 6-->1 hydrogen-bonded conformations, reminiscent of helix-terminating structural features in proteins. The crystal parameters for the three peptides, Boc-Val-Aib-X-Aib-Ala-Aib-Y-OMe, where X and Y are Phe, Leu (I), Leu, Phe (II) and Leu, Leu (III) are: (I) space group P1, Z = 1, a = 9.903 A, b = 10.709 A, c = 11.969 A, alpha = 102.94 degrees, beta = 103.41 degrees, gamma = 92.72 degrees, R = 4.55%; (II) space group P21, Z = 2, a = 10.052 A, b = 17.653 A, c = 13.510 A, beta = 108.45 degrees, R = 4.49%; (III) space group P1, Z = 2 (two independent molecules IIIa and IIIb in the asymmetric unit), a = 10.833 A, b = 13.850 A, c = 16.928 A, alpha = 99.77 degrees, beta = 105.90 degrees, gamma = 90.64 degrees, R = 8.54%. In all cases the helices form 3(10)/alpha-helical (or 3(10)helical) structures, with helical columns formed by head-to-tail hydrogen bonding. The helices assemble in an all-parallel motif in crystals I and III and in an antiparallel motif in II. In the four crystallographically characterized molecules, I, II, IIIa and IIIb, Aib(6) adopts a left-handed helical (hL) conformation with positive phi, psi values, resulting in 6-->1 hydrogen-bond formation between Aib(2) CO and Leu(7)/Phe(7) NH groups. In addition a 4-->1 hydrogen bond is seen between Aib(3) CO and Aib(6) NH groups. This pattern of hydrogen bonding is often observed at the C-terminus of helices proteins, with the terminal pi-type turn being formed by four residues adopting the hRhRhRhL conformation.

Interaction of 5-Hydroxy-L-Tryptophan with Deoxyribonucleic Acid and Nucleohistone

The binding of 5-hydroxy-L-tryptophan (HT), a radioprotector, with deoxyribonucleic acid (DNA) and deoxyribonucleohistone (DNH) in 2.5 × 10 -4 MEDTA and 0.9% sodium chloride solutions takes place in the concentration ratio of (a) DNA : HT 25μg/ml : 20-25 μg/ml and (b) DNH : HT 25 μg/ml : 20-25 μg/ml. Analytical evidences show that the modes of binding are by (i) electrostatic interaction (ii) ion condensation (iii) staking and (iv) intercalation. The two solvents EDTA and 0.9% sodium chloride affect the degree of dissociation of DNA and DNH to different extent, and hence attachment mode of HT with these bioplaymers is decided by stereospecific accessibility. The functional groups responsible for binding are phenolic OH,(indole), (side chain of HT), phosphate groups and phosphodiester bond for DNA, and CONH group, lysine and arginine and chromophores like: -C=C-C=N and -C=C-C=O for DNH. The method of calculations of the binding has been given.

CCK-B agonist or antagonist activities of structurally hindered and peptidase-resistant Boc-CCK4 derivatives.

Replacement of Met31 by (N-Me)Nle in CCK8 or CCK4 has been shown to improve the affinity and selectivity for CCK-B receptors. In order to obtain molecules with enhanced bioavailability, two novel series of protected tetrapeptides of the general formula Boc-Trp30-X-Asp-Y33 have been developed. Introduction of (N-Me)Nle and the bulky, aromatic naphthylalaninamide (Nal-NH2) in positions X and Y, respectively, does not greatly modify the affinity for guinea pig brain CCK-B receptors. In contrast, incorporation of hindering N-methyl amino acids such as (N-Me)Phe, (N-Me)Phg, or (N-Me)Chg, but not their non-methylated counterparts, in position X induced a large decrease in affinity for the CCK-B binding sites. Among the various peptides synthesized, Boc-[(N-Me)Nle31,1Nal-NH2(33)]CCK4 (2) (KI = 2.8 nM), Boc-[Phg31,1Nal-NH2(33)]CCK4 (15) (KI = 14 nM), and Boc-[Phg31,1Nal-N(CH3)2(33)]CCK4 (17) (KI = 39 nM) displayed good affinities for brain CCK-B receptors and had good selectivity ratios. These pseudopeptides, in which the presence of unnatural and hydrophobic residues is expected to improve their penetration of the central nervous system, were shown to be very resistant to brain peptidases. Interestingly, whereas compounds 2 and 15 proved to be full agonists for rat hippocampal CCK-B receptors when measured in an electrophysiological assay, compound 17 behaved as a potent antagonist in the same test and displayed a good affinity in rat brain KI(CCK-B) = 51 nM as compared to the Merck antagonist L365,260,KI(CCK-B) = 12 nM. This illustrates a simple means to obtain CCK-B antagonists and suggests that the free, CONH2 group plays a critical role in the recognition of the agonist state of brain CCK-B receptors.

Binding of metal cations by N-carboxymethyl chitosans in water

The binding of metal cations by N-carboxymethyl chitosan in dilute aqueous solution was studied as a function of charge density, temperature and pH. The techniques employed were absorption and circular dichroism measurements, potentiometric titration, dilatometry and isothermal microcalorimetry. The composition of the polymer significantly affected the binding of Ni(II), Co(II) and Pb(II), and had a small influence on the extent of binding of Cu(II). In any case, the density of glycine residues affected the binding constant with all the counterions studied, thus confirming that this residue is engaged in the complex formation. The whole of the optical, chirooptical and thermodynamic evidence showed that, at least in the case of Cu(II), the ions are bound by both carboxylic and amino groups. The temperature did not affect the extent of binding, at least in the case of Cu(II) and Pb(II) ions. Circular dichroism spectra, however, showed that these counterions are able to interact with NHCOgroups at high temperatures (61°C), very likely owing to the enhanced mobility of the polymer chain. Lowering pH depressed the binding ability of N-carboxymethyl chitosan towards Cu(II) and Pb(II) ions, the effect being much more pronounced in the case of Pb(II). Moreover, a refined method for collecting absorption spectra of the complex between the polymer and Cu(II) or Pb(II) ions, without interference with absorbance by undesired species, was tested and applied. The charge-transfer band exhibited by the N-carboxymethyl chitosan-Cu(II) system, recorded following this method, showed interesting features, on the basis of which the site of the binding of Cu(II) on to N-carboxymethyl chitosan was confirmed.

Thermodynamic properties of N-octyl-, N-decyl- and N-dodecylpyridinium chlorides in water

Densities, heat capacities and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for N-octyl-, N-decyl- and N-dodecyl-pyridinium chlorides in water over a wide concentration region. Conductivity measurements were performed in order to evaluate the cmc and the degree of counterion dissociation. Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25°C were derived from the experimental data as functions of the surfactant concentration. The changes with concentration of these properties are quite regular with the exception of the heat capacities which display anomalies at about 0.9, 0.25 and 0.12 mol-kg−1 for the octyl, decyl and dodecyl compounds, respectively. At these concentrations there were also changes in the slopes of the specific conductivity and of the product of the osmotic coefficients and the molality vs. concentration. These peculiarities can be ascribed to micelle structural transitions. The thermodynamic functions of micellization were graphically evaluated on the basis of the pseudo-phase transition model. These data have been compared to those for alkyltrimethylammonium bromides and alkylnicotinamide chlorides. It is shown that the introduction of the hydrophilic CONH2 group lowers the hydrophilic character of the pyridinium ring.

Reaction of tetrafluorodibenz[b,f][1,4]oxazepin-11(10H)-ones with nucleophiles

Reaction of 1,2,3,4-tetrafluorodibenz[b,f][1,4]oxazepin-11(10H)-one with nucleophilic reagents (MeONa in refluxing MeOH; piperidine in DMF at 100‡C) leads to substitution of the fluorine atom para to the CONH group. 6,7,8,9-Tetrafluorodibenz[b,f][1,4]oxazepin-11(10H)-one is inert to these conditions.

Conformational Structure of an L-Asparagine/L-Aspartate Random Copolypeptide as Revealed by Vibrational and CD Spectroscopy

The infrared and Raman spectra of an L-asparagine/L-aspartate random copolypeptide with an L-asparagine residue content of 69% mol have been measured in aqueous solution and in the solid state and analyzed for the first time. The infrared amide I, I', and II bands have been related to the conformational structure of the polypeptide backbone with the aid of CO spectroscopy, whereby it has been concluded that this biopolymer adopts a random coiled secondary structure. The backbone conformation remains unordered even when side-chain carboxyl groups are in the undissociated form (-COOH). The fact that this polypeptide takes this secondary structure in preference to α-helices and β-sheets can be explained by weak hydrophobic bonding between side chains and/or by hydrogen bonding between peptide CONH groups and side-chain polar groups. Another interesting site is the amide III Raman region, which in spite of the above results shows a band in the range usually attributed to α-helical structure. This finding is due to contributions from methine bonds and CH2 groups and indicates that the side chains can influence the position of the bands in the amide III region. Consequently, this result reveals that associating polypeptide backbone conformation with characteristic frequency ranges in the amide III region may be incorrect.

Crystal structure and solution conformation of S,S′‐bis(Boc‐Cys‐Ala‐OMe): Intramolecular antiparallel β‐sheet conformation of an acyclic cystine peptide

The conformation of the acyclic biscystine peptide S,S'-bis(Boc-Cys-Ala-OMe) has been studied in the solid state by x-ray diffraction, and in solution by 1H- and 13C-nmr, ir, and CD methods. The peptide molecule has a twofold rotation symmetry and adopts an intramolecular antiparallel beta-sheet structure in the solid state. The two antiparallel extended strands are stabilized by two hydrogen bonds between the Boc CO and Ala NH groups [N...O 2.964 (3) A, O...HN 2.11 (3) A, and NH...O angle 162 (3) degrees]. The disulfide bridge has a right-handed conformation with the torsion angle C beta SSC beta = 95.8 (2) degrees. In solution the presence of a twofold rotation symmetry in the molecule is evident from the 1H- and 13C-nmr spectra. 1H-nmr studies, using solvent and temperature dependencies of NH chemical shifts, paramagnetic radical induced line broadening, and rate of deuterium-hydrogen exchange effects on NH resonances, suggest that Ala NH is solvent shielded and intramolecularly hydrogen bonded in CDCl3 and in (CD3)2SO. Nuclear Overhauser effects observed between Cys C alpha H and Ala NH protons and ir studies provide evidence of the occurrence of antiparallel beta-sheet structure in these solvents. The CD spectra of the peptide in organic solvents are characteristic of those observed for cystine peptides that have been shown to adopt antiparallel beta-sheet structures.

Difffrences in sequence selectivity of DNA alkylation by isomeric intercalating aniline mustards

Two DNA-targeted mustard derivatives, N,N-bis(2-chloroethyl)-4-(5-[9-acridinylamino]-pentamido)aniline and 4-(9-[acridinylamino]butyl 4-( N,N-bis[2-chloroethyl]-aminobenzamide, which are isomeric compounds where the mustard is linked to the DNA-binding 9-aminoacridine moiety by either a -CONH- or a -NHCO- group, show significant differences in the sequence selectivity of their alkylation of DNA. The CONH isomer is a more efficient alxylating agent than the NHCO compound by an order of magnitude, consistent with the larger electron release of the CONH group to the aniline ring. However, the pattern of alkylation by the two compounds is also very different, with the CONH isomer preferring alkylation of guanines adjacent to 3′- or 5′-adenines and cytosines (for example those in sequences 5′-CGC, 5′-AGC, 5′-CGG and 5′-AGA) while the isomeric NHCO compound shows preference for guanines in runs of Gs. In addition, both isomers alkylate 3′-adenines in runs of adenines. Both compounds also show completely different patterns of alkylation to their untargetted mustard counterparts, since 4-MeCONH-aniline mustard alkylates all guanines and adenines in runs of adenines, while 4-Me 2NCO-aniline mustard fails to alkylate DNA at all. These differences in alkylation patterns between the CONH- and its isomeric NHCO- compounds and their relationships between the alkylation patterns of the isomers and their biological activities are discussed.

Hydrophobicity of N‐Acetyl‐Di‐ and Tripeptide Amides Having Unionizable Side Chains and Correlation with Substituent and Structural Parameters

AbstractThe log P value of 53 N‐acetyl‐di‐ and tripeptide amides composed of amino acids having unionizable side chains was measured in a 1‐octanol/pH 7.0 aqueous buffer system. The factors governing the variations in the log P value among these protected peptides were quantitatively analyzed to formulate a correlation equation with free‐energy‐related physicochemical and substructural parameters. The log P value was governed by the sum of the hydrophobicity of side chains and the backbone as well as by the steric effects of side chain substituents on the relative solvation of the backbone CONH groups. The log P value was found to decrease by 0.6 log unit for the peptide bond, other factors being equal. For amino acids with polar side chains, the log P value was also affected by the “polar proximity factor” and/or intramolecular hydrogen bond formation in a way similar to that of zwitterionized peptides reported previously.

Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos

AbstractA now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.

Prototropic reactions for 1-, 2-, and 4-fluorenamides in the ground and excited singlet states

Absorption and fluorescence spectra of 1-, 2- and 4-fluorenamides (1-FAm, 2-FAm, 4-FAm) were studied in different solvents and at various acid concentrations. This study indicates that the long wavelength absorption band is long-axis polarised in 2-FAm whereas in 1-FAm and 4-FAm, it is composed of long- and short-axis polarised transitions. The —CONH2 group in 1-FAm and 4-FAm is coplanar with the fluorene moiety, whereas the same group in 2-FAm is non-coplanar with the fluorene ring in non-polar solvents, both in S0 and S1 states, but attains coplanarity in the polar and hydrogen bonding solvents in the S1 state. Hammett's acidity scale is not valid for the protonation reaction of amides and a medium effect is observed on the absorption spectra of the monocations in strong sulphuric acid. The prototropic equilibrium for the protonation of ring carbon atom is not established in the S1 state, due to the slower rate of protonation reaction. Proton-induced fluorescence quenching of the monocations is followed before the monocations are being protonated.

Crystal structures of azo pigments derived from acetoacetanilide

The crystal structures often azo pigments derived from acetoacetanilide have been determined by single crystal X‐ray diffraction techniques. A review of these crystal structures indicates the existence of certain common features. It is found that, in the solid state, the molecules do not exist in the azo form but in the form of the hydrazone tautomer. The hydrogen in the hydrazone group and the one in the CONH group both take part in intramolecular hydrogen bonding. In both cases the hydrogen bond may be bifurcated (shared) between two acceptor atoms. These intramolecular hydrogen bonds hold the molecule more or less planar. In general the molecules stack in columns and these columns are linked by van der Waals forces, but in a minority of cases (three out often) intermolecular hydrogen bonds have been found. A relationship between molecular stacking and crystal morphology is pointed out.

Synthetic peptide models for the redox-active disulfide loop of glutaredoxin. Conformational studies.

Two cyclic peptide disulfides (Sequence: see text). (X = L-Tyr or L-Phe) have been synthesized as models for the 14-membered redox-active disulfide loop of glutaredoxin. 1H NMR studies at 270 MHz in chloroform solutions establish a type I beta-turn conformation for the Pro-X segment in both peptides, stabilized by a 4----1 hydrogen bond between the Cys(1) CO and Cys(4) NH groups. Nuclear Overhauser effects establish that the aromatic ring in the X = Phe peptide is oriented over the central peptide unit. In dimethyl sulfoxide solutions two conformational species are observed in slow exchange on the NMR time scale, for both peptides. These are assigned to type I and type II beta-turn structures with -Pro-Tyr(Phe)- as the corner residues. The structural assignments are based on correlation of NMR parameters with model 14-membered cyclic cystine peptides with Pro-X spacers. Circular dichroism studies based on the -S-S- n-omega* transition suggest a structural change in the disulfide bridge with changing solvent polarity, establishing conformational coupling between the peptide backbone and the disulfide linkage in these systems.

Probing peptide backbone function in bombesin. A reduced peptide bond analogue with potent and specific receptor antagonist activity.

Each peptide bond CONH group in the most important COOH-terminal octapeptide region of [Leu14]bombesin was replaced by a CH2NH group using recently developed rapid solid-phase methods. The resulting analogues were then examined for amylase releasing activity in guinea pig pancreatic acini and for their ability to inhibit binding of [125I-Tyr4]bombesin to acinar cells. Replacement of the Trp8-Ala9, Gly11-His12, and His12-Leu13 peptide bonds resulted in about 1000-, 200-, and 300-fold losses in both amylase releasing activity and binding affinity. The Val10-Gly11 replacement, however, retained 30% potency relative to the parent peptide. Ala9-Val10 and Leu13-Leu14 bond replacement analogues exhibited no detectable amylase releasing activity but were still able to bind to acini with Kd values of 1060 and 60 nM, respectively (compared to 15 nM for [Leu14]bombesin itself). Subsequently, both analogues were demonstrated to be competitive inhibitors of bombesin-stimulated amylase release with IC50 values of 937 and 35 nM, respectively. [Leu14-psi-CH2NH-Leu13]Bombesin exhibits a 100-fold improvement in binding affinity compared to previously reported bombesin receptor antagonists and showed no affinity for substance P receptors. It was also a potent inhibitor of bombesin-stimulated growth of murine Swiss 3T3 cells with an IC50 of 18 nM. In terms of a bombesin receptor-binding conformation, these results may aid in the delineation of intramolecular hydrogen-bonding points and the eventual design of improved, conformationally restricted analogues.