Angiotensin Peptides as AT2 Receptor Agonists.

In 2004, the first nonpeptide selective angiotensin II type 2 receptor (AT2R) agonist was reported. This nonpeptide (C21), which, exerts anti-inflammatory and antifibrotic actions in vivo, has been extensively explored and is currently in clinical trials. Subsequently, a large number of related drug-like AT2R agonists have been disclosed. Reviews that summarize known structure-activity relationships (SAR) of nonpeptide AT2R agonists have recently appeared in the literature; however, very few reviews discuss the role of angiotensin peptides as AT2R agonists. Furthermore, to date, there have been no reports focusing on the medicinal chemistry perspective of peptide AT2R agonists. In the present review, reports on linear and conformationally constrained Ang II analogues, with a focus on AT2R selective ligands that are proven to act as agonists at the AT2 receptor are summarized. The impact of truncations and macrocyclizations of Ang II analogues and of incorporation of scaffolds that mimic secondary structures into Ang II related peptides is highlighted. A survey of the efforts to transform the nonselective octapeptide Ang II to more drug-like selective AT2R agonists is presented. The relationship between the structures of the AT2R agonists and their affinity to the AT2R is briefly discussed and common pharmacophore elements of AT2R selective Ang II peptide analogues and selective nonpeptide AT2R agonists are compared.

Angiotensin II analogues with N-terminal lactam bridge cyclization: an overview on AT1 receptor activation and tachyphylaxis.

Angiotensin II (AngII) is the final active product of the renin enzymatic cascade, which is responsible for sustaining blood pressure. To investigate the effect of N-terminal cyclization on AT1 activation and tachyphylaxis, we designed conformationally constrained analogues with an i-(i + 1) lactam bridge. All analogues presented the same binding coefficient and tachyphylactic index, but some of them such as Cyclo (0-1a) [Glu0 , endo-(Lys1a )]-AngII and Cyclo (0-1a) [Asp0 , endo-(Orn1a )]-AngII showed higher potency. The same tachyphylactic index presented by AngII and cyclic analogues was surprising. We expected a variation after the modification of AngII N-terminal region.

Evidences for the action mechanism of angiotensin II and its analogs on Plasmodium sporozoite membranes.

Malaria is an infectious disease responsible for approximately one million deaths annually. Oligopeptides such as angiotensin II (AII) and its analogs are known to have antimalarial effects against Plasmodium gallinaceum and Plasmodium falciparum. However, their mechanism of action is still not fully understood at the molecular level. In the work reported here, we investigated this issue by comparing the antimalarial activity of AII with that of (i) its diastereomer formed by only d-amino acids; (ii) its isomer with reversed sequence; and (iii) its analogs restricted by lactam bridges, the so-called VC5 peptides. Data from fluorescence spectroscopy indicated that the antiplasmodial activities of both all-D-AII and all-D-VC5 were as high as those of the related peptides AII and VC5, respectively. In contrast, retro-AII had no significant effect against P. gallinaceum. Conformational analysis by circular dichroism suggested that AII and its active analogs usually adopted a ß-turn conformation in different solutions. In the presence of membrane-mimetic micelles, AII had also a ß-turn conformation, while retro-AII was random. Molecular dynamics simulations demonstrated that the AII chains were slightly more bent than retro-AII at the surface of a model membrane. At the hydrophobic membrane interior, however, the retro-AII chain was severely coiled and rigid. AII was much more flexible and able to experience both straight and coiled conformations. We took it as an indication of the stronger ability of AII to interact with membrane headgroups and promote pore formation.

Effects of the angiotensin II Ala-scan analogs in erythrocytic cycle of Plasmodium falciparum (in vitro) and Plasmodium gallinaceum (ex vivo).

The anti-plasmodium activity of angiotensin II and its analogs have been described in different plasmodium species. Here we synthesized angiotensin II Ala-scan analogs to verify peptide-parasite invasion preservation with residue replacements. The analogs were synthesized by 9-fluorenylmethoxycarbonyl (Fmoc) and tert-butyloxycarbonyl (t-Boc) solid phase methods, purified by liquid chromatography and characterized by mass spectrometry. The results obtained in Plasmodium falciparum assays indicated that all analogs presented some influence in parasite invasion, except [Ala(4)]-Ang II (18% of anti-plasmodium activity) that was not statistically different from control. Although [Ala(8)]-Ang II presented a lower biological activity (20%), it was statistically different from control. The most relevant finding was that [Ala(5)]-Ang II preserved activity (45%) relative to Ang II (47%). In the results of Plasmodium gallinaceum assays all analogs were not statistically different from control, except [Ala(6)]-Ang II, which was able to reduce the parasitemia about 49%. This approach provides insight for understanding the importance of each amino acid on the native Ang II sequence and provides a new direction for the design of potential chemotherapeutic agents without pressor activity.

Antiplasmodial activity study of angiotensin II via Ala scan analogs.

Angiotensin II (AII) as well as analog peptides shows antimalarial activity against Plasmodium gallinaceum and Plasmodium falciparum, but the exact mechanism of action is still unknown. This work presents the solid-phase synthesis and characterization of eight peptides corresponding to the alanine scanning series of AII plus the amide-capped derivative and the evaluation of the antiplasmodial activity of these peptides against mature P. gallinaceum sporozoites. The Ala screening data indicates that the replacement of either the Ile(5) or the His(6) residues causes minor effects on the in vitro antiplasmodial activity compared with AII, i.e. AII (88%), [Ala(6) ]-AII (79%), and [Ala(5) ]-AII (75%). Analogs [Ala(3) ]-AII, [Ala(1) ]-AII, and AII-NH2 showed antiplasmodial activity around 65%, whereas the activity of the [Ala(8) ]-AII, [Ala(7) ]-AII, [Ala(4) ]-AII, and [Ala(2) ]-AII analogs is lower than 45%. Circular dichroism data suggest that AII and the most active analogs adopt a ß-fold conformation in different solutions. All AII analogs, except [Ala(4) ]-AII and [Ala(8) ]-AII, show contractile responses and interact with the AT1 receptor, [Ala(5) ]-AII and [Ala(6) ]-AII. In conclusion, this approach is helpful to understand the contribution of each amino acid residue to the bioactivity of AII, opening new perspectives toward the design of new sporozoiticidal compounds.

A mild removal of Fmoc group using sodium azide.

A mild method for effectively removing the fluorenylmethoxycarbonyl (Fmoc) group using sodium azide was developed. Without base, sodium azide completely deprotected N (α)-Fmoc-amino acids in hours. The solvent-dependent conditions were carefully studied and then optimized by screening different sodium azide amounts and reaction temperatures. A variety of Fmoc-protected amino acids containing residues masked with different protecting groups were efficiently and selectively deprotected by the optimized reaction. Finally, a biologically significant hexapeptide, angiotensin IV, was successfully synthesized by solid phase peptide synthesis using the developed sodium azide method for all Fmoc removals. The base-free condition provides a complement method for Fmoc deprotection in peptide chemistry and modern organic synthesis.

Bivalent angiotensin II suppresses oxidative stress-induced hyper-responsiveness of angiotensin II receptor type I.

Angiotensin II receptor type I (AT1R) is a G-protein coupled receptor involved in regulation of body water-electrolyte balance and blood pressure. Oxidative stress promotes AT1R oligomerization and hyper-responsiveness to its cognate ligand Ang II. In this study, bivalent Ang II, synthesized by linking with aminocaproic acid (Acp) at the N-terminus, was used to induce AT1R dimerization and hyper-responsiveness in AT1R-expressed human embryonic kidney (AT1R-HEK) cells, determined using image correlation spectroscopy (ICS) and by measuring AT1R-mediated change in intracellular Ca(2+) concentration, respectively. In addition, ICS was employed to determine distribution pattern of cell-surface AT1R and its degree of aggregation when stimulated by monomeric (monovalent) and bivalent Ang II under oxidative stress (100 µM H2O2) condition in comparison with normal (unoxidized) AT1R-HEK cells. Bivalent Ang II induced cell-surface AT1R aggregation/clustering but maintained AT1R normal signaling response under oxidative stress condition, whereas stimulation by monomeric Ang II or a mixture of monomeric and Acp-modified Ang II (used in the synthesis of bivalent form) resulted in AT1R hyper-responsiveness. These results suggest that bivalent ligand (viz. Ang II) provides another strategy in the development of novel drugs specifically designed for attenuating aberrant responsiveness of cognate receptor (AT1R) under pathological (oxidative stress) conditions.

Central administration of angiotensin IV rapidly enhances novel object recognition among mice.

Angiotensin IV (Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) has demonstrated potential cognitive-enhancing effects. The present investigation assessed and characterized: (1) dose-dependency of angiotensin IV's cognitive enhancement in a C57BL/6J mouse model of novel object recognition, (2) the time-course for these effects, (3) the identity of residues in the hexapeptide important to these effects and (4) the necessity of actions at angiotensin IV receptors for procognitive activity. Assessment of C57BL/6J mice in a novel object recognition task demonstrated that prior administration of angiotensin IV (0.1, 1.0, or 10.0, but not 0.01 nmol, i.c.v.) significantly enhanced novel object recognition in a dose-dependent manner. These effects were time dependent, with improved novel object recognition observed when angiotensin IV (0.1 nmol, i.c.v.) was administered 10 or 20, but not 30 min prior to the onset of the novel object recognition testing. An alanine scan of the angiotensin IV peptide revealed that replacement of the Val(1), Ile(3), His(4), or Phe(6) residues with Ala attenuated peptide-induced improvements in novel object recognition, whereas Tyr(2) or Pro(5) replacement did not significantly affect performance. Administration of the angiotensin IV receptor antagonist, divalinal-Ang IV (20 nmol, i.c.v.), reduced (but did not abolish) novel object recognition; however, this antagonist completely blocked the procognitive effects of angiotensin IV (0.1 nmol, i.c.v.) in this task. Rotorod testing demonstrated no locomotor effects with any angiotensin IV or divalinal-Ang IV dose tested. These data demonstrate that angiotensin IV produces a rapid enhancement of associative learning and memory performance in a mouse model that was dependent on the angiotensin IV receptor.

Disulfide cyclized tripeptide analogues of angiotensin IV as potent and selective inhibitors of insulin-regulated aminopeptidase (IRAP).

The insulin-regulated aminopeptidase (IRAP) localized in areas of the brain associated with memory and learning is emerging as a new promising therapeutic target for the treatment of memory dysfunctions. The angiotensin II metabolite angiotensin IV (Ang IV, Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) binds with high affinity to IRAP and inhibits this aminopeptidase (K(i) = 62.4 nM). Furthermore, Ang IV has been demonstrated to enhance cognition in animal models and is believed to play an important role in cognitive processes. It is herein reported that displacement of the C-terminal tripeptide His(4)-Pro(5)-Phe(6) with a phenylacetic acid functionality combined with a constrained macrocyclic system in the N-terminal affords potent IRAP inhibitors that are less peptidic in character than the hexapeptide Ang IV. Configurational analysis of three pairs of diastereomeric Ang IV analogues was performed using a combination of solution NMR spectroscopic methods, Monte Carlo conformational searches, and NAMFIS calculations. The compounds encompassing l-amino acids only (4, 8, and 12) showed significantly higher bioactivity compared to their lld-epimers (5, 9, and 13). The best inhibitors in the series, compounds 8 and 12, incorporating a 13- and 14-membered disulfide ring system, respectively, and both with a ß(3)-homotyrosine residue (ß(3)hTyr) replacing Tyr(2), exhibit K(i) values of 3.3 and 5.2 nM, respectively.

Conformational properties of angiotensin II and its active and inactive TOAC-labeled analogs in the presence of micelles. Electron paramagnetic resonance, fluorescence, and circular dichroism studies.

The interaction between angiotensin II (AII, DRVYIHPF) and its analogs carrying 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) and detergents--negatively charged sodium dodecyl sulfate (SDS) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS)--was examined by means of EPR, CD, and fluorescence. EPR spectra of partially active TOAC1-AII and inactive TOAC3-AII in aqueous solution indicated fast tumbling, the freedom of motion being greater at the N-terminus. Line broadening occurred upon interaction with micelles. Below SDS critical micelle concentration, broader lines indicated complex formation with tighter molecular packing than in micelles. Small changes in hyperfine splittings evinced TOAC location at the micelle-water interface. The interaction with anionic micelles was more effective than with zwitterionic micelles. Peptide-micelle interaction caused fluorescence increase. The TOAC-promoted intramolecular fluorescence quenching was more pronounced for TOAC3-AII because of the proximity between the nitroxide and Tyr4. CD spectra showed that although both AII and TOAC1-AII presented flexible conformations in water, TOAC3-AII displayed conformational restriction because of the TOAC-imposed bend (Schreier et al., Biopolymers 2004, 74, 389). In HPS, conformational changes were observed for the labeled peptides at neutral and basic pH. In SDS, all peptides underwent pH-dependent conformational changes. Although the spectra suggested similar folds for AII and TOAC1-AII, different conformations were acquired by TOAC3-AII. The membrane environment has been hypothesized to shift conformational equilibria so as to stabilize the receptor-bound conformation of ligands. The fact that TOAC3-AII is unable to acquire conformations similar to those of native AII and partially active TOAC1-AII is probably the explanation for its lack of biological activity.

Beta-homo-amino acid scan of angiotensin IV.

Angiotensin IV, a metabolite of angiotensin II, inhibits the enzyme insulin regulated aminopeptidase or IRAP and also, although with lower potency, aminopeptidase-N (AP-N). When both beta (2)-homo amino acid- and beta (3)-homo amino acid substitutions were used, allowed the identification of H-( R)beta (2)hVal-Tyr-Ile-His-Pro-beta (3)hPhe-OH as a potent and stable Ang IV analog with high selectivity for IRAP versus AP-N and the AT1 receptor.

Comprimidos de liberación inmediata de Valsartán y Efavirenz: el papel de la concentración de superdisgregantes / Immediate release tablets of Valsartan and Efavirenz: role of concentration of superdisintegrants

El objetivo de este estudio fue formular comprimidos de rápida disgregación, obtenidos mediante compresión directa,de fármacos con baja solubilidad en agua y diferentes grados de solubilidad, tomando como modelo Valsartány Efavirenz. Se estudió el efecto de diversas concentraciones de diferentes superdisgregantes como crospovidona,croscarmelosa sódica y glicolato sódico de almidón sobre el tiempo de disgregación y la disolución del fármaco invitro. Se observó que el tiempo de disgregación del comprimido con mejor liberación inmediata, de entre todaslas formulaciones probadas, fue de 21,5 ± 1,26 s y 20,16 ± 0,85 s para los comprimidos de Valsartán y Efavirenz,respectivamente que contenían, en ambos casos, un 20% de crospovidona. La liberación del fármaco (tanto en loscomprimidos de Valsartán como Efavirenz) fue más rápida en el caso de las formulaciones con crospovidona encomparación con la otra formulación. El efecto fue más evidente en el caso de Efavirenz, cuya solubilidad en aguaes menor que la de Valsartán. Se observó que era necesario un 20% de crospovidona para obtener una liberacióndel fármaco del 80% en comprimidos de Efavirenz. Los estudios por calorimetría diferencial de barrido no indicaronninguna incompatibilidad fármaco-excipiente. En conclusión, se obtuvieron por compresión directa comprimidosde rápida disgregación de Valsartán y Efavirenz con tiempos de disgregación más cortos y una alta velocidad dedisolución. Además, la crospovidona resultó ser un mejor disgregante tanto para Valsartán como para Efavirenz,de acuerdo con el tiempo de disgregación y los valores T80% obtenidos

The objective of this study was to formulate directly compressible fast disintegrating tablets of poorly water solubledrugs with different extent of drug solubilities, like valsartan and efavirenz, as model drugs. Effect of varying concentrationsof different superdisintegrants such as crospovidone, croscarmellose sodium, and sodium starch glycolate ondisintegration time and in vitro drug dissolution was studied. The disintegration time of the best immediate release tabletformulation among those tested was observed to be 21.5±1.26 sec and 20.16±0.85 sec for valsartan and efavirenz tabletscontaining 20% of Crospovidone, respectively. Drug release (from both valsartan and Efavirenz tablets) was faster fromformulations containing crospovidone compared to the other formulation. The effect was more apparent in Efavirenz,which has lesser aqueous solubility than valsartan. It was observed that 20% crospovidone was required to achieve80% drug release from efavirenz tablets. Differential scanning calorimetric studies did not indicate any drug-excipientincompatibility. In conclusion, directly compressible fast disintegrating tablets of valsartan and efavirenz with shorterdisintegration times and high dissolution rate were obtained and crospovidone seemed to be a better disintegrant forboth valsartan and efavirenz, based on disintegration time and T80% values obtained (AU)

Small potent ligands to the insulin-regulated aminopeptidase (IRAP)/AT(4) receptor.

Angiotensin IV analogs encompassing aromatic scaffolds replacing parts of the backbone of angiotensin IV have been synthesized and evaluated in biological assays. Several of the ligands displayed high affinities to the insulin-regulated aminopeptidase (IRAP)/AT(4) receptor. Displacement of the C-terminal of angiotensin IV with an o-substituted aryl acetic acid derivative delivered the ligand 4, which exhibited the highest binding affinity (K(i) = 1.9 nM). The high affinity of this ligand provides support to the hypothesis that angiotensin IV adopts a gamma-turn in the C-terminal of its bioactive conformation. Ligand (4) inhibits both human IRAP and aminopeptidase N-activity and induces proliferation of adult neural stem cells at low concentrations. Furthermore, ligand 4 is degraded considerably more slowly in membrane preparations than angiotensin IV. Hence, it might constitute a suitable research tool for biological studies of the (IRAP)/AT(4) receptor.

Stereospecific synthesis of a carbene-generating angiotensin II analogue for comparative photoaffinity labeling: improved incorporation and absence of methionine selectivity.

A stereospecific convergent synthesis of N-[(9-fluorenyl)methoxycarbonyl]-p-[3-(trifluoromethyl)-3H-diazirin-3-yl]-l-phenylalanine (Fmoc-12, Fmoc-Tdf) and its incorporation into the C-terminal position of the angiotensin II (AngII) peptide to form (125)I[Sar(1),Tdf(8)]AngII ((125)I-13) is presented. This amino acid photoprobe is a highly reactive carbene-generating diazirine phenylalanine derivative that can be used for photoaffinity labeling. Using model receptors, we compared the reactivity and the Met selectivity of 12 to that of the widely used and reputedly Met-selective p-benzoyl-l-phenylalanine (Bpa) photoprobe. Wild-type and mutant AngII type 2 receptors, a G protein-coupled receptors, were photolabeled with (125)I-13 as well as with (125)I[Sar(1),Bpa(8)]AngII ((125)I-14), and the respective incorporation yields were assessed. The carbene-generating 12 was more reactive toward inert residues and was not Met-selective compared to the biradical ketone-generating Bpa, allowing for more precise determination of ligand contact points in peptidergic receptors.

Angiotensin II pseudopeptides containing 1,3,5-trisubstituted benzene scaffolds with high AT2 receptor affinity.

Two 1,3,5-trisubstituted aromatic scaffolds intended to serve as gamma-turn mimetics have been synthesized and incorporated in five pseudopeptide analogues of angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe), replacing Val-Tyr-Ile, Val-Tyr, or Tyr-Ile. All the tested compounds exhibited nanomolar affinity for the AT2 receptor with the best compound (3) having a K(i) of 1.85 nM. Four pseudopeptides were AT2 selective, while one (5) also exhibited good affinity for the AT1 receptor (K(i) = 30.3 nM). This pseudopeptide exerted full agonistic activity in an AT2 receptor induced neurite outgrowth assay but displayed no agonistic effect in an AT1 receptor functional assay. Molecular modeling, using the program DISCOtech, showed that the high-affinity ligands could interact similarly with the AT2 receptor as other ligands with high affinity for this receptor. A tentative agonist model is proposed for AT2 receptor activation by angiotensin II analogues. We conclude that the 1,3,5-trisubstituted benzene rings can be conveniently prepared and are suitable as gamma-turn mimics.

Bioconjugates for tunable peptide fragmentation: free radical initiated peptide sequencing (FRIPS).

The free radical initiator Vazo 68 is coupled to a peptide and electrosprayed into an ion trap mass spectrometer. On collisional activation, the Vazo 68-peptide conjugate generates a free radical, which can be collisionally activated to cleave the peptide backbone. Mostly z-type fragments are formed, as in CAD of other radical peptides and ECD fragmentation. We present data for the Angiotensin II-Vazo 68 conjugate and discuss possible sites of H atom abstraction from the peptide. This experimental methodology for generating peptide fragments is a useful step toward the development of a completely gas-phase approach to protein sequencing.

A emergência de um novo modulador cardiovascular - a 2ªenzima de conversão da angiotensina 2 (ECA2) / The emergenceof a new cardiovascular modulator 2ªangiostensin-converting enzyme 2 (ACE2)

O sistemarenina-angiotensina (SR-A) exerce um papel central no controle das várias alças de regulação cardiovascular. Muito dos seus efeitos são modulados pela enzima conversora de angiotensina (ECA) que remove dois aminoácidos da angiotensina I para formar a angiotensina II (AngII). A Ang II é o vasoconstrictor mais potente entre os que participam da fisiopatogenia da hipertensão arterial. Outros produtos do SR-A também contribuem para os mecanismos reguladores da perfusão tecidual. É o caso da angiotensina(1-7), gerada diretamente da Ang I por endopeptidases, e que é um potente vasodilatador, opondo-se às ações tróficas da Ang II. A partir de 2000, uma outra enzima do SR-A foi caracterizada; sua sequência genômica apresentou várias semelhanças estruturais com o gene da ECA humana. Por isso, foi denominada ECA2. É expressa principalmente pelas células endoteliais, coração e rim. A ECA2 tem atividades biológicas distintas da ECA, convertendo a Ang I em Ang(1-9), que é subsequentemente hidrolisada pela ECA em Ang(1-7). A ECA2 hidrolisa a Ang II, produzindo, também, a partir daí, a Ang II, produzindo, também, a partir daí, a Ang(1-7). A ECA2, além de ser uma enzima chave na geração de um potente vasodilatador [Ang(1-7)], é essencial para uma adequada função miocárdica. A perspectiva de se contar com uma droga que especificamente induza à formação de ECA2, atenuando, ao mesmo tempo, a atividade da Ang II poderá abrir novos horizontes terapêuticos para a hipertensão arterial e doenças cardiovasculares

AT2-selective angiotensin II analogues containing tyrosine-functionalized 5,5-bicyclic thiazabicycloalkane dipeptide mimetics.

This paper reports the synthesis of two angiotensin II analogues with tyrosine-functionalized 5,5-bicyclic thiazabicycloalkane dipeptide mimetics replacing the Tyr(4)-Ile(5) residues. The preparation of these analogues relies on the synthesis and incorporation of an alpha,alpha-disubstituted chimeric amino acid derivative and on-resin bicyclization to a cysteine residue. The synthesized analogues both displayed high angiotensin AT(2)/AT(1) receptor binding preferences and had AT(2) receptor affinities in the same low nanomolar range as angiotensin II itself. Conformational analysis, using experimental constraints derived from NMR studies, indicated that the Tyr(4) and His(6) residues in one of the angiotensin II analogues were in close proximity to each other.

A selective AT2 receptor ligand with a gamma-turn-like mimetic replacing the amino acid residues 4-5 of angiotensin II.

Three angiotensin II (Ang II) analogues encompassing a benzodiazepine-based gamma-turn-like scaffold have been synthesized. Evaluation of the compounds in a radioligand binding assay showed that they had no affinity to the rat liver AT(1) receptor. However, one of the compounds displayed considerable affinity to the pig uterus AT(2) receptor (K(i) = 3.0 nM) while the other two lacked affinity to this receptor. It was hypothesized that the reason for the inactivity of one of these analogues to the AT(2) receptor was that the guanidino group of the Arg(2) residue and/or the N-terminal end of the pseudopeptide could not interact optimally with the receptor. To investigate this hypothesis, a conformational analysis was performed and a comparison was carried out with the monocyclic methylenedithioether analogue cyclo(S-CH(2)-S)[Cys(3,5)]Ang II which is known to bind with high affinity to the AT(2) receptor (K(i) = 0.62 nM). This comparison showed that, in the compounds with high AT(2) receptor affinity, the guanidino group of the Arg(2) residue and the N-terminal end could access common regions of space that were not accessible to the inactive compound. To examine the importance of the guanidino group for binding, the Arg side chain was removed by substituting Arg(2) for Ala(2) in the analogue having the high affinity. This analogue lacked affinity to AT(2) receptors, which supports the role of the guanidino group in receptor binding.

Use of commercial anion-exchange resins as solid support for peptide synthesis and affinity chromatography.

This report demonstrates that due to the presence of residual reactive sites in their matrices, classical diethylaminoethyl-attaching commercial anion-exchanger resins such as DEAE-MacroPrep and DEAE-Sephadex A50 supports can be used for peptide synthesis. Moreover, due to the high stability of the peptide-resin bond in the final cleavage treatments, desired peptidyl-resins free of side-chain protecting groups, which enables them to be further used as solid support for affinity chromatography, can be obtained. To demonstrate this potentiality, a fragment corresponding to the antigenic and immunodominant epitope of sporozoites of the Plasmodium falciparum malaria parasite was synthesized in these traditional resins and antibody molecules generated against the peptide sequence were successfully retained in these peptidyl supports. Due to the maintenance of their original anion-exchange capacities, the present findings open the unique possibility of applying, simultaneously, dual anion-exchange and affinity procedures for purification of a variety of macromolecules.