DL-2-Amino-4-phosphonobutyric acid, an isostere of phosphoserine, was incorporated into the heptapeptide sequence, Leu-Arg-Arg-Ala-(DL-2-amino-4-phosphonobutyric acid)-Leu-Gly, for kinetic mechanistic studies of the cAMP-dependent protein kinase. To block the phosphono hydroxyl groups, methyl, ethyl and 4nitrobenzyl esters were studied as possible protecting groups. The phosphono diethyl ester of the N-Fmoc-protected amino acid was utilized in the synthesis of the heptapeptide. Two configurational forms of the protected peptide were obtained and were separated by C18-reverse phase HPLC. Characterization of the two isomeric forms was accomplished by 3 1P NMR, 1H NMR, 13C% NMR and amino acid analysis. The protecting groups of the isomeric phsophonopeptides were removed by HBr/AcOH and purified by cation exchange HPLC. Both phosphonopeptides were found to be inhibitors of the cAMP-dependent protein kinase, having Ki values of 0.6 mM (peptide A) and 1.9 mM (peptide B).

Due to increased plant resistance to the existing antibiotics produced, there is a need to develop alternatives. Nonribosomal peptides (NRPs) are important plant phytopathogens synthesized by nonribosomal peptide synthetases (NRPSs). In this study, a newly sequenced Bacillus strain Bacillus atrophaeus UCMB 5137 (63Z), found to have increased phytopathogenic activity, was investigated to gain insights to the possible reason behind this activity. NRPS modules were identified using a novel script that can act on unannotated, raw DNA sequences. The Structure Based Sequence Analysis Webserver was used to identify the amino acids incorporated into the final NRP, which were compared to the NRP database. Five NRPSs were found within the strain; fengycin/plipstatin, mycosubtilin, surfactin, bacillibactin and bacitracin. Some of the modules usually present for these NRPSs were not present in the test strain and only a few modules were found. A phylogenetic study was carried out and the topologies of the trees showed that genes were not transferred horizontally. It did, however, lead to the hypothesis that different NRPS genes are under different adaptive evolutionary pressures. Only slight conformational changes between L and D-conformation of amino acids were seen between the test and neighboring strains. All of the linker and terminal regions of synthetases were found to exhibit a large amount of conservation overall. Homology modeling was performed on the test strain on selected modules, TE and A-domains of fengycin and mycosubtilin synthetases. TE-domains between the different synthetases are different and specific for the NRP they facilitate release for. The NRPS from which the A-domain originates also influences substrate specificity as well as the module in which the A-domain occurs within the NRPS. Binding pockets of A-domains of differing substrate specificity were compared. Future work will include; refinement of the models and docking studies within the A-domain binding pocket. / Microsoft� Word 2010 / Adobe Acrobat 9.54 Paper Capture Plug-in

Cyclic dipeptides have been well characterized for their multitude of biological activities, including antimicrobial and anticancer activities. Cyclo(His-Gly) and cyclo(His-Ala) have also recently been shown to possess significant anticancer activity against a range of cell lines, despite the limitations of these two molecules with respect to their physicochemical properties. Low Log P results in poor cell permeability which can often be problematic for drugs with intracellular mechanisms of action. It can also results in poor biodistribution, and theoretical Log P values for cyclo(His-Gly) and cyclo(His-Ala) were extremely low making them ideal candidates for inclusion into a nanoparticulate drug delivery system. The aim of this study was therefore to formulate and evaluate liposome-encapsulated cyclic dipeptides that increase the tumour-suppressive actions of the cyclic dipeptides, while showing a high degree of specificity for tumour cells. While liposomes are relatively simple to prepare, inter batch variation, low encapsulation and poor stability are often problematic in their production and this has lead to very few liposomal products on the market. This study aimed at using a comprehensive statistical methodology in optimizing liposome formulations encapsulating cyclo(His-Gly) and cyclo(His-Ala). Initial screening of potential factors was conducted using a 25-1 fractional factorial design. This design made use of two levels for each of the five factors and abbreviated the design to minimize runs. Although not much information is provided by these types of designs, the design was sufficient in identifying two critical factors that would be studies further in a more robust design. The two factors selected, based on the screening study, were cholesterol and stearylamine content. These two factors were then used in designing a response surface methodology (RSM) design making use of a central composite rotatable vii design (CCRD) at five levels (-1.5, -1, 0, 1, 1.5) for each factor in order to better understand the design space. Various factors influenced the measured responses of encapsulation efficiency, zeta potential, polydispersity index, cellular uptake and leakage, but most notable were the adverse effects of increasing stearylamine levels on encapsulations efficiency and cholesterol levels on leakage for both cyclo(His-Gly) and cyclo(His-Ala) liposomes. Optimized formulations were derived from the data and prepared. Fair correlation between the predicted and measured responses was obtained. The cytotoxic activity of the encapsulated cyclic dipeptides were assessed against HeLa and MCF-7 cells and found to have limited improvement in activity. However, modification of the polyethylene glycol (PEG) grafted to the liposome surface in order to target folate receptors showed good benefit in significantly decreasing the IC50 values recorded in all cells lines tested, particularly low folate HeLa cells with the lowest IC50 being recorded as 0.0962 mM for folate targeted cyclo(His-Ala). The results therefore indicate that hydrophilic cyclic dipeptides are ideal candidates for inclusion into targeted drug delivery systems such as liposomes. Key words: Liposomes, cyclo(His-Gly), cyclo(His-Ala), cyclic dipeptides, HeLa, MCF-7, folate receptors, factorial design, response surface methodology (RSM), central composite rotatable design (CCRD).

Indiana University-Purdue University Indianapolis (IUPUI) / The DNA minor groove continues to be an important biological target in the development of anticancer, antiviral, and antimicrobial compounds. Among agents that target the minor groove, studies of well-established benzimidazole-based DNA binders such as Hoechst 33258 have made it clear that the benzimidazole-amidine portion of these molecules promotes an efficient, site-selective DNA association. Building on the beneficial attributes of existing benzimidazole-based DNA binding agents, a series of benzimidazole-amino acid conjugates was synthesized to investigate their DNA recognition and binding properties. In this series of compounds, the benzimidazole-amidine moiety was utilized as a core DNA “anchoring” element accompanied by different amino acids to provide structural diversity that may influence DNA binding affinity and site-selectivity. Single amino acid conjugates of benzimidazole-amidines were synthesized, as well as a series of conjugates containing 20 dipeptides with the general structure Xaa-Gly. These conjugates were synthesized through a solid-phase synthetic route building from a resin-bound amino acid (or dipeptide). The synthetic steps involved: (1) the coupling of 4-formylbenzoic acid to the resin-bound amino acid (via diisopropylcarbodiimide and hydroxybenzotriazole); followed by (2) introduction of a 3,4-diaminobenzamidoxime in the presence of 1,4-benzoquinone to construct the benzimidazole ring; and, finally, (3) reduction of the resin-bound amidoxime functionality to an amidine via treatment with 1M SnCl2•2H2O in DMF before cleavage of final product from the resin. The synthetic route developed and employed was simple and straightforward except for the final reduction that proved to be very arduous. All target compounds were obtained in good yield (based upon weight), averaging 73% mono-amino acid and 78% di-amino acid final compound upon cleavage from resin. Ultimately, the DNA binding activities of the amino acid-benzimidazole-amidine conjugates were analyzed using a fluorescent intercalator displacement (FID) assay and calf thymus DNA as a substrate. The relative DNA binding affinities of both the mono- and di-amino acid-benzimidazole-amidine conjugates were generally weaker than that of netropsin and distamycin with the dipeptide conjugates showing stronger binding affinities than the mono-amino acid conjugates. The dipeptide conjugates containing amino acids with positively charged side chains, Lys-Gly-BI-(+) and Arg-Gly-BI-(+), showed the strongest DNA binding affinities amongst all our synthesized conjugates.

Contemporary developments in the field of synthetic peptide methodologies are imperative for enabling the advance of drug design in medicinal chemistry. Although many groundbreaking discoveries have been made in this field in the past few decades, there has only been a recent renaissance in transition metal catalyzed methods which create unnatural amino acids and generate macrocyclic peptide structures. Rh(III)-catalyzed methods which install C-C bonds and C-N bonds across readily available alkene substrates have been an underexplored avenue for peptide modification chemistry. In this thesis, several novel catalytic methodologies are disclosed which simultaneously install unnatural amino acid motifs during peptide ligation events. In Chapter 3, we report a modular peptide ligation methodology that couples dioxazolones, arylboronic acids, and acrylamides to construct amide bonds in a diastereoselective manner under mild conditions, facilitated by Rh(III) catalysis. In Chapter 4, we disclose a Rh(III)-catalyzed macrocyclization via carboamidation, reacting acryloyl-peptide-dioxazolone precursors and arylboronic acids to form complex cyclic peptides with concomitant incorporation of noncanonical α-amino acids. In Chapter 5, we describe ongoing efforts to develop a complementary Rh(III)-catalyzed hydroamidation reaction which furnishes macrocyclic peptides to expand the chemical space in which complex peptidomimetic molecules can be attained.

No description available.

This thesis set out to explore the conformational properties of short designed peptide sequences, in which transitions between structural states may be anticipated. The use of conformationally constrained residues like α-aminoisobutyric acid (Aib) and D-proline (DPro) permits the design of model sequences for structural studies. The principle of imposing conformational constraints by multiple substitutions at backbone atoms in aminoacid residues may also be extended to the higher homologs of α-amino acids, namely β and residues. The experimental results presented in this thesis also examine the potential of using cross-strand interactions between aromatic residues as a probe of structure in designed peptide β-hairpins. Chapter 1 provides a very brief introduction to the necessary background on which the experimental studies in this thesis are based. Chapter 2 describes studies aimed at establishing chain length effects on helix-hairpin conformational distributions in short synthetic sequences, containing centrally positioned Aib-DAla and Aib-Aib segments.The Aib-DAla dipeptide segment has a tendency to form both type-I'/III' and type-I/III β-turns. The occurrence of prime turns facilitates the formation of β-hairpin conformations, while type-I/III turns can nucleate helix formation. The octapeptide Boc-Leu-Phe-Val-Aib-DAla-Leu-Phe-Val-OMe (1) has been previously shown to form a β-hairpin in the crystalline state and in solution. The effects of sequence truncation have been examined using the model peptides Boc-Phe-Val-Aib-Xxx-Leu-Phe-NHMe (2, 6), Boc-Val-Aib-Xxx-Leu-NHMe (3, 7) and Boc-Aib-Xxx-NHMe (4, 8), where Xxx = DAla, Aib. For peptides with central Aib-Aib segments, Boc-Phe-Val-Aib-Aib-Leu-Phe-NHMe (6), Boc-Val-Aib-Aib-Leu-NHMe (7) and Boc-Aib-Aib-NHMe (8) local helical conformations have been established by NMR studies in both hydrogen bonding (CD3OH) and non-hydrogen bonding (CDCl3) solvents. In contrast, the corresponding hexapeptide Boc-Phe-Val-Aib-DAla-Leu-Phe-Val-NHMe (2) favors helical conformations in CDCl3 and β-hairpin conformations in CD3OH. β-Turn conformations (type-I /III) stabilized by intramolecular 4 1 hydrogen bonds are observed for the peptide Boc-Aib-DAla-NHMe (4) and Boc-Aib-Aib-NHMe (8) in crystals. The tetrapeptide Boc-Val-Aib-Aib-Leu-NHMe (7) adopts an incipient 310-helical conformation stabilized by three 4 1 hydrogen bonds. The peptide Boc-Val-Aib-DAla- Leu-NHMe (3) adopts a novel -turn conformation, stabilized by three intramolecular hydrogen bonds (two 4 1 and one 5 1). The Aib-DAla segment adopts a type-I' β-turn conformation. The observation of the NOE Val(1) NH HNCH3 (5), in CD3OH, suggests that the solid state conformation of peptide 3 is maintained in methanol solutions. Peptide hairpins provide an ideal scaffold for exploring cross-strand interactions between residues on facing antiparallel strands. Chapter 3 reports studies directed towards probing, aromatic interactions between facing Phe residues, positioned at the non-hydrogen bonding positions in designed octapeptide β-hairpins. The studies described in this Chapter employ ring current shifted aromatic proton resonances as a means of probing aromatic ring orientations. Crystal structures of eight peptide -hairpins with the sequence Boc-Leu-Phe-Val-Xxx-Yyy-Leu-Phe-Val-OMe revealed that the Phe(2) and Phe(7) aromatic rings are in close spatial proximity, with a centroid-centroid distance (Rcen) of 4.4Å to 5.4Å between the two phenyl rings. Proton NMR spectra in chloroform and methanol solutions reveal a significant upfield shift of the Phe(7) C , ′ H2 protons (6.65 ppm to 7.04 ppm). Specific assignments of the aromatic protons have been carried out in the peptide Boc-Leu-Phe-Val-DPro-LPro-Leu-Phe-Val-OMe (6). The anticipated ring current shifts have been estimated from the aromatic ring geometries observed in crystals for all eight peptides. Only one of the C , ′ H proton lies in the shielding zone, with rapid ring flipping, resulting in averaging between the two extreme chemical shifts. An approximate estimate of the population of conformations which resemble crystal state orientations may be obtained. Key nuclear Overhauser effects (NOEs) between facing Phe sidechains provide support for close similarity between the solid state and solution conformations. Temperature dependence of aromatic ring proton chemical shifts and line widths for peptide 6 (Boc-Leu-Phe-Val-DPro-LPro-Leu-Phe-Val-OMe) and the control peptide Boc-Leu-Val-Val-DPro-Gly-Leu-Phe-Val-OMe establish an enhanced barrier to ring flipping, when the two Phe rings are in proximity. Modeling studies suggest that small, conformational adjustments about the C -C ( 1), and C -C ( 2) bonds of the Phe residues may be required in order to permit unhindered, uncorrelated flipping of both the Phe rings. The maintenance of specific aromatic ring orientations in organic solvents provides evidence for significant stabilizing interactions. Earlier studies from this laboratory established that a centrally positioned DPro-LPro-DAla segment could induce hairpin formation in nonapeptide sequences, facilitated by a three residue loop segment. The DAla residue at position 6 in the nonapeptide Boc-Leu-Phe-Val-DPro-LPro-DAla-Leu-Phe-Val-OMe has been shown to adopt a left handed helical (αL) conformation. The studies described in Chapter 4, examine the effects of aminoacid replacements at positions 5 and 6. NMR studies on eight nonapeptides, with the general sequence Boc-Leu-Phe-Val-DPro-Xxx-Yyy-Leu-Phe-Val-OMe are described. In the case of peptides with a central DPro-LPro-Yyy sequence, two kinds of hairpin conformations are formed in solution. These are; i) β-hairpin structures with a central three residue loop, resulting in registered antiparallel tripeptide strands, and ii) a slipped hairpin structure, nucleated by a central DPro-LPro type-II β-turn, with residue 6 being incorporated into the C-terminal strand. The three residue loop β-hairpins are favored for DAla(6) and Aib(6), while the LAla(6) peptide favors a “slipped” hairpin structure. Replacement of the Pro(5) residue by LAla results in a reduced population of three residue hairpins in the nonapeptide with the DPro-LAla-DAla segment. Replacement of Pro(5) by Aib, abolished hairpin formation. Aromatic proton chemical shifts provide a convenient diagnostic for the presence of three residue loop hairpin conformations in these nonapeptides. A great deal of current interest has focused on the conformations of peptides incorporating β and γ aminoacid residues. Earlier studies from this laboratory have focused on the conformational properties of the β,β -disubstituted γ residue gabapentin (1-aminomethylcyclohexane acetic acid). Subsequent work with the related β aminoacid β3,3Ac6c (1-aminocyclohexaneacetic acid) revealed that intramolecularly hydrogen bonded conformations are infrequently observed in short peptides. The studies described in Chapter 5, examine the conformational properties for model peptides containing the isomeric β-aminoacid, β2,2Ac6c (1-aminomethylcyclohexane-1-carboxylic acid). The effect of gem dialkyl substituents on the backbone conformations of amino acid residues in peptides, has been investigated using four model peptides, Boc-Xxx-2,2Ac6c-NHMe [Xxx = Leu (1), Phe(2)] and Boc-Xxx- 3,3Ac6c-NHMe [Xxx = Leu (3), Phe(4)]. Tetrasubstituted carbon atoms restrict the ranges of stereochemically allowed a C11 helical turn, which is a backbone expanded analog of the type III -turn in sequences. The crystal structure of the peptide Boc-Phe- 3,3Ac6c-NHMe (4) establishes a the asymmetric unit adopt backbone torsion angles of opposite signs. In one of the molecules, the Phe residue adopts an unfavourable backbone conformation, with the energetic penalty being offset by favourable aromatic interactions between proximal molecules in the crystal. NMR studies provide evidence for the maintenance of folded structures in solution, in these hybrid sequences. The result presented in this thesis suggests that it should be possible to construct designed synthetic peptides, which can undergo transitions between two distinct and energetically favourable conformational states. The ability to design peptide sequences that can undergo switching between helical and β-hairpin states, or between hairpin structures with variations in connecting loop length may prove valuable in providing further insights into the factors influencing conformational dynamics.

Made available in DSpace on 2015-07-22T20:50:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-27. Added 1 bitstream(s) on 2015-08-11T03:25:32Z : No. of bitstreams: 1 Publico-00399a.pdf: 1787027 bytes, checksum: 6cb684251c1894e3685b611ace5c9056 (MD5). Added 1 bitstream(s) on 2015-08-11T03:25:32Z : No. of bitstreams: 2 Publico-00399a.pdf: 1787027 bytes, checksum: 6cb684251c1894e3685b611ace5c9056 (MD5) Publico-00399b.pdf: 1285455 bytes, checksum: 52050426f68cebcd4b7e00081ce49a38 (MD5). Added 1 bitstream(s) on 2015-08-11T03:25:32Z : No. of bitstreams: 3 Publico-00399a.pdf: 1787027 bytes, checksum: 6cb684251c1894e3685b611ace5c9056 (MD5) Publico-00399b.pdf: 1285455 bytes, checksum: 52050426f68cebcd4b7e00081ce49a38 (MD5) Publico-00399c.pdf: 2029206 bytes, checksum: 480bbfb2deea834d9cc92a52def4805e (MD5) / A gomesina (Gm) é um potente peptídeo antimicrobiano catiônico. Este peptídeo e seu análogo linear [Ser2,6,11,15]-Gm, com menor atividade lítica, foram sintetizados pela metodologia da fase sólida, empregando-se a estratégia t-Boc. Neste estudo, investigamos a interação da Gm e da [Ser2,6,11,15]-Gm com vesículas unilamelares gigantes (GUVs), compostas por membranas lipídicas de POPC ou POPC/POPG, através de microscopias óticas de contraste de fase e fluorescência. As análises se dividiram em duas diferentes partes. Na primeira, observou-se o efeito da injeção de uma solução peptídica, com micropipeta, na vizinhança das GUVs. Como resultado da interação peptídeo/lipídio, as GUVs foram desestabilizadas e romperam-se rapidamente, sem observação de formação de poros estáveis durante todo o experimento. Nos estudos controles, em ausência de peptídeo, as GUVs não romperam de forma espontânea. Peptídeos marcados com a sonda fluorescente rodamina (Rh) foram injetados e mostram que a Gm primeiramente acumula-se na superfície da vesícula, na qual, então, pequenas partículas de alto-contraste são formadas e ocorre, eventualmente, a destruição das GUVs. Este fato leva-nos a especular que a Gm rompe as membranas via modo carpete. Na segunda parte, uma solução contendo GUVs foi misturada a crescentes concentrações peptídicas para quantificação da ação lítica destes peptídeos em vesículas de diferentes composições lipídicas. O efeito de atividade lítica observado foi maior que 90% em baixas concentrações tanto de Gm quanto de [Ser2,6,11,15]-Gm em GUVs compostas de POPC, lipídio eletricamente neutro, e de uma mistura de POPG, negativamente carregados, a POPC em diferentes proporções. Estudos conformacionais foram feitos por duas técnicas espectroscópicas distintas: dicroísmo circular (CD) e fluorescência. A Gm e seu análogo linear aparentemente interagiram com as cargas negativas de SDS nas concentrações acima e abaixo da CMC. Os espectros de CD da [Ser2,6,11,15]-Gm em água apresentaram uma banda fortemente negativa em 198 nm, indicando tratar-se de uma estrutura desordenada, como esperado para peptídeos livres em solução, e não de uma dobra beta como apresentada pela Gm. A partir dos resultados obtidos, foi possível concluir que ambos os peptídeos analisados interagem com vesículas compostas por fosfolipídios e induzem o vazamento de seu conteúdo interno dependentemente da carga de membrana destas, o que corrobora estudos prévios que sugerem que as interações eletrostáticas com a bicamada lipídica dos micro-organismos representam um importante papel no mecanismo de ação da Gm. / TEDE / BV UNIFESP: Teses e dissertações

La Maladie d’Alzheimer est caractérisée par la formation de dégénérescences neurofibrillaires, constituées de protéine Tau anormalement hyperphosphorylée et agrégée. De nombreuses études traitent de possibles stratégies thérapeutiques basées sur l’inhibition de cette polymérisation, et présentent les effets bénéfiques de certaines molécules dont les polyphénols, mais les résultats obtenus jusque là, manquent de données au niveau moléculaire. Ainsi, après avoir synthétisé, une banque de polyphénols de structures différentes, et 3 peptides représentatifs de la région P de phosphorylation de Tau, c’est en suivant une stratégie combinant la RMN et la modélisation moléculaire, que nous avons évalué les paramètres dynamiques du complexe formé. Ce projet nous a apporté des informations en termes d’affinité, et de relations structure/activité et ainsi, de mieux appréhender les mécanismes d’interactions intervenant dans l’agrégation de Tau par les polyphénols. / Alzheimer's disease is characterized by the formation of neurofibrillary tangles constituted by abnormally hyperphosphorylated and aggregated Tau protein. Many studies deal with potential therapeutic strategies based on the inhibition of this polymerization, and show the beneficial effects of some molecules like polyphenols, but the obtained so far results show a lack of data at the molecular level. Thus, after the synthesis of, a library of polyphenols with different structures, and 3 representative peptides of the P2 phosphorylation Tau region, by following a strategy combining NMR and molecular modeling, we have evaluated dynamic parameters of the formed complex. This project has provided us informations in terms of affinity, and structure / activity relationships, and leading us to a better understanding of the mechanisms led to better understand the mechanisms involved in the aggregation Tau inhibition phenomena by polyphenols.

Proteínas e peptídeos ricos em glicina são encontrados em animais e plantas. Alguns apresentam atividade antimicrobiana. Como pouco se sabe sobre suas síntese, estrutura, relação estrutura-atividade e mecanismo de ação, tais tópicos foram estudados para os antimicrobianos cheferina I (Chef I) e/ou fragmentos da acantoscurrina (acanto). No que se refere à Chef I (67,9% de Gly, 28,6% de His, seis repetições do motivo GGH e uma Tyr), sintetizamos, purificamos, caracterizamos e testamos Chef I, os seus análogos truncados na(s) porção(ções) N- ou/e C-terminal (is) e os análogos amidados Chef la, Chef I (3-28)a e Chef I (6-28)a. Os três últimos e Chef I foram igualmente ativos frente a cepas de C. albicans (MIC: 12,5 µM), mas não frente a cepas de C. tropicalis e S. cerevisiae. A amidação tornou o análogo Chef I (3-28)a mais ativo frente a tais cepas. Enquanto as atividades antifúngicas de Chef la e de seus análogos foram reduzidas pelo aumento da força iônica, elas foram aumentadas em presença de ZnCl2 5-10 µM. A 62,5 µM a Chef la foi letal para C. albicans MDM8. Ela foi pouco hemolítica em tampão fosfato contendo NaCl ou em tampão glicose fosfato isotônico (100 µM: 18%). Análises por microscopia confocal e citometria de fluxo revelaram que Chef la marcada com carboxifluoresceína (FAM-Chef la) foi rapidamente internalizada nas células de C. albicans MDM8, um processo que não foi afetado pela força iônica do meio e se mostrou dependente de ATP e temperatura. Quanto aos fragmentos da acanto (proteína com 132 aminoácidos, 73% de Gly e 3 repetições de uma seqüência de 26 aminoácidos), estudamos a síntese em fase sólida dos fragmentos N- e C-terminais, acanto (1-22) e acanto (101-132) , respectivamente, e da porção repetitiva, acanto (23-48). Apesar de uma predição teórica não ter indicado alto potencial de agregação para a acanto, as sínteses foram problemáticas: a ocorrência de aminoacilações incompletas repetitivas a 60° C usando diferentes estratégias, resinas, reagentes acopladores, solventes e sais caotrópicos sugeriram a ocorrência de agregação das cadeias peptídicas em crescimento sobre as resinas O uso da resina CLEAR amida permitiu a obtenção do acanto (113-132). Tentativa de síntese convergente em fase sólida não foi bem sucedida. Espectros Raman das peptidil-resinas obtidas confirmaram a presença de estruturas em folha β pregueada. Somente o uso combinado de resina CLEAR amida, 60°C, 20% DMSO/NMP, Fmoc-(Fmoc-Hmb)Gly-OH e LiCI permitiram a síntese total de acanto (101-132) . O uso da resina CLEAR ácida permitiu a síntese do fragmento acanto (23-48) e acanto (10-22) , esta última durante a tentativa de síntese do acanto (1-22) . Os rendimentos foram baixissimos e os espectros Raman das peptidil-resinas correspondentes também indicaram a formação de folhas β pregueadas. Estes resultados indicaram que Chef I (3-28)a mimetiza Chef I, que Chef la é um fungicida potente com alvo intracelular, que a internalização do seu análogo marcado na célula de levedura ocorra via endocitose, que a Chef la tem potencial para agir como uma droga de uso tópico e que os fragmentos de acanto são \"difficult sequences\" típicas. / Proteins and peptides with high content of glycine have been found in animais and plants. Some of them display antimicrobial activity. As little is known about their chemical synthesis, structure, structure-activity relationship and mode of action, we studied such topics using shepherin I (Shep I) and fragments of acanthoscurrin (acantho) as targets. Concerning to Shep I (67.9% of Gly, 28.6% of His, six direct repeats of the motif GGH and one Tyr), we synthesized, purified, characterized and tested Shep I, its analogues truncated at the N- and/or C-terminal portions and the amidated analogues Shep la, Shep I (3-28)a and Shep I (6-28)a. The last three analogues and Shep I were equally active against C. albicans (MIC: 12.5 µM) strains, but not against C. tropicalis and S. cerevisiae strains. Cterminal amidation made Shef I (3-28)a more active against those fungai strains. Anticandidal activities of Shep la and truncated analogues were inhibited in high ionic strength solutions, but enhanced at 10 µM ZnCI (2 to 8-fold). At 62.5 µM (5 MIC), Shep la killed C. albicans MDM8 in 30 mino It caused low hemolysis in phosphate buffered saline and isotonic glucose phosphate buffer (100 µM: 18%). Confocal microscopy and flow cytometry analyses revealed that Shep I modified with carboxyfluorescein (FAM-Shep la) was rapidly internalized into C. albicans MDM8 cells, process not affected by ionic strength and showed to be energy and temperature-dependent. As to the fragments of acantho (a protein with 132 amino acids, 73% of Gly, and three repeats of 26 amino acids), we studied solid-phase syntheses of the N- and C-terminal portions, acantho (1-22) and acantho (101-132), respectively, and of the repetitive portion, acantho (23-48). A theoretical prediction did not indicate high aggregation potential for acantho, but solid-phase syntheses were troublesome: repetitive incomplete aminoacylations took place even at 60°C using different strategies, resins, coupling reagents, solvents and chaotropic salts, suggesting aggregation of the growing peptide chains. Change to CLEAR amide resin allowed obtaining acantho (113-132) . Attempt using convergent solid phase synthesis was not successful. Raman spectra of the growingpeptidyl-resins revealed pleated β-sheet structures. Only the combination of CLEAR amide resin, 60°C, 20% DMSO/NMP, Fmoc-(Fmoc-Hmb)Gly-OH and LiCl allowed the total synthesis of acantho (101-132). The use of CLEAR acid resin also allowed obtaining the fragments acantho (23-48) and acantho (10-22), the last one during the attempt of the synthesis of acantho (1-22). The synthesis yields were extremely low and, again, the Raman spectra of the growing peptide-resins indicated the occurrence of pleated β-sheet structures. Altogether, the results indicated that Shep l (3-28)a mimics the fungicidal activity of Shep l, Shep la is a potent anticandidacidal peptide that has an intracellular target, FAM Shep la may be internalized into the fungai cells via endocytosis, Shep la has the potential to act as a drug for topical use and acantho fragments are typical difficult sequences.