Total Synthesis of the α‐Helical Eicosapeptide Antibiotic Alamethicin

Abstract

The voltage-dependent membrane pore-forming polypeptide antibiotic alamethicin F 30 (Ac-Aib-Pro-Aib-Ala-Aib-Ala-Gln-Aib-Val-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-Glu-Gln-Phl, 1) was synthesiied by segment condensations. It was obtained free of racemate (<0.8% o-components) via the segments 2-11 (4a) and 12-20 (3a) using the dicyclohexylcarbodiimide/l-hydroxybenzotriazole and the mixed anhydride methods. The intermediates were unequivocally characterized by chromatographic and physical methods including I3C NMR, circular dichroism, and chiral phase gas chromatography. The segments 2 -6 (Sa) and 12 -20 (3) were also proven by X-ray structure determinations. -The final product 1 (150 mg) was obtained without HPLC separations in very high purity and in crystalline form. According to all analytical data and the comparison by spectroscopy and chromatographic analyses (HPLC, DC) the product 1 is identical with the main component F 30 of the microheterogeneous antibiotic metabolite isolated from Trichoderma tliride. The antibiotic activities of synthetic alamethicin (I) and the stimulating effect on calcium/calmodulin-dependent guanylate cyclase of Paramecium are identical with those of natural alamethicin. -The uniform synthetic alamethicin (1) shows perfectly homogeneous conductance states of single pores on measurements in lipid bilayer membranes which had not been reported so far for any synthetic or purified natural preparation. Totalsynthese des a-helikalen Eikosapeptid-Anlibiotikums Alamethicin *)Das spannungsabhangige Mernbranporen-bildende Polypeptidantibiotikum Alamethicin F 30 (Ac-Aib-Pro-Aib-Ala-Aib-Ala-Gln-Aib-Val-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-Glu-Gln-Phl, 1) wurde durch Segmentkondensationen synthetisiert. Es wurde uber die Segmente 2-11 (4a) und 12 -20 (3a) racematfrei (<0.8% D-Anteile) mit der Dicyclohexylcarbodiimid/l-Hydroxybenzotriazol-und der Mischanhydrid-Methode erhalten. Die Zwischenstufen wurden eindeutig charakterisiert durch chromatographische und physikalische Methoden einschlieBlich I3C-NMR, Circulardichroismus und Gaschromatographie an chiraler Phase. Die Segmente 2 -6 (Sa) und 12 -20 (3) wurden auch durch Rontgenstrukturbestimmung untersucht. -Das Endprodukt 1 (1 50 mg) wurde ohne HPLC-Trennung in sehr hoher Reinheit und kristallin erhalten. Nach allcn analytischen Daten und bei spektroskopischem und chromatographischem (HPLC, DC) Vergleich ist das Produkt 1 identisch mit der Hauptkomponente F 30 des mikroheterogenen, aus Trichoderma ciride isolierten antibiotischen Metaboliten. Die antibiotischen Aktivitaten von synthetischem * ) Results of this synthesis including I3C NMR and single pore measurements of synthetic alamethicin were reported on the following symposia:Alamethicin (1) und die stimulierende Wirkung auf die Calcium/Calmodulin-abhangige Guanylatcyclase von Paramecium sind identisch niit denen von natiirlichem Alamethicin. -Das einheitliche synthetische Alamethicin (1) zeigt bei Messungen an Lipiddoppelschicht-Membranen perfekt homogene Leitwerte von Einzelporen, wie sie bisher weder v...

The chemistry of peptides related to metabolites of Trichoderma Spp. 3. An unusual dehydration reaction of 2-methylalanine peptides after electron impact ionization

“…All were homogeneous on reverse phase partition chromatography and the retention volumes measured are given in crystalline peptides were hydrated, the water of hydration being tenaciously held. This unexpected phenomenon was reported recently for an analogous compound (14).…”

“…The data in Tables 1 and 2 (8) is 23, but for the pentapeptide with the C-terminus 2-methylalanyl-2-methylalanylglutamate (6), the ratio is 3. The NH group between two 2-methylalanine residues is not readily exchanged (14), and in our hands cannot be methylated except under forcing conditions when C-methylation also occurs. The data in Table 1 therefore support the hypothesis that the probability of dehydration depends on the steric hindrance of the 2-methylalanyl NH group.…”

The chemistry of peptides related to metabolites of Trichoderma spp. 2. An improved method of characterization of peptides of 2-methylalanine

“…1 l), the suzukacillins (6), and the alamethicins (12) are very complex mixtures and that the proportions of the individual components of the mixture depend on the conditions of growth of the producing fungus. These facts and the worldwide interest in the physiological properties of these materials have led to extraordinary synthetic efforts to obtain a single entity by synthesis (13)(14)(15)(16)(17). The results of these efforts in the alamethicin field have been symmarized by Schmidt and Jung (16), who show that the measurements of the physical properties of the synthetic products by the different groups fall outside normally accepted ranges of error.…”

“…These facts and the worldwide interest in the physiological properties of these materials have led to extraordinary synthetic efforts to obtain a single entity by synthesis (13)(14)(15)(16)(17). The results of these efforts in the alamethicin field have been symmarized by Schmidt and Jung (16), who show that the measurements of the physical properties of the synthetic products by the different groups fall outside normally accepted ranges of error. The structures of many of the intermediates in the syntheses have been established by detailed assignment of 'H and I3C nmr spectra (see e.g., ref.…”

Konvergenz führt zum Erfolg: Totalsynthese des komplexen nicht‐ribosomalen Peptids Polytheonamid B

“…Diese Arbeit steht damit in der Nachfolge anderer Meilensteine der Peptid-Synthese, z. B. der Synthese des Membranporen bildenden Antibiotikums Alamethicin [10] und des DNA-Gyrase-Inhibitors Microcin. [11] Im Falle von Polytheonamid B (1) …”