Antamanide

Antamanide is a lipophilic neutral compound that forms colorless crystals which are easily soluble in alcohols but almost insoluble in water it has a molecular mass of 1147 (mass spectroscopy). On hydrolysis, antamanide is spHt to yield the L-amino acids alanine, valine, phenylalanine, proline in a molar ratio of 1 1 4 4. Its structure, determined by gas chromatographic separation of the fragments obtained by partial methanolysis and their analysis by mass spectroscopy is displayed in Fig. 17. 

The appearance of an ion corresponding to AA-Na in the mass spectrum was the first indication of ion-complexes of the cyclopeptide. An increase of carbonyl adsorption in the presence of Na in the infrared spectra, showed that the peptide interacts with cations through its amide carbonyl groups. The stability of AA-complexes with various cations was then determined, by various physical methods with the result that it exhibits the order of preference. 

Antamanide exerts its protective effect against phalloidin (PHD) (see p. 217) in mice when given one hour before or at the latest simultaneously with the drug. Five milligram PHD per kg body weight will kill a white mouse within 2-4 hours with certainty but the animal is fully protected from death by 0.6 mg AA per kg. 

Shortly after its structure had been determined syntheses of AA were described. In the laboratory of one of the authors, two pentapeptide segments consisting of amino acids Nos. 6-10 and 1-5 were synthesized mainly by the mixed anhydride method (p. 79), connected to form a linear decapeptide which, after deprotection of its ends, was cyclized (Fig. 18). 

The solid phase technique of Merrifield (Chap. 5) proved very useful for obtaining a series of analogs of AA which were compared with respect to their antitoxic activities, ion binding capacities and molecular structures. 

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Wieland, T., et al. Identity of hepatic membrane transport systems for bile salts, phalloidin, and antamanide by photoaffinity labeling. Proc. Natl. Acad. Sci. U. S. A. 1984, 81, 5232-5236. 

Fig. 11.11 13C and 15N MAS spectra of antama-nide for different sample preparations, a Lyophi-lized powder, b and c Micro-crystalline powder obtained by evaporation of the solvent from a solution of antamanide in a 7 3 methanol/water mixture. In the 13C spectra, only the aliphatic region is shown. The sample leading to spectra b was... 

Fig. 11.13 An N(CO)CA spectrum of the decapep- these two spectra in a stepwise fashion as inditide antamanide (contours) together with the cated by the arrows, all 15N and 13C resonances...

Antamanide, a cyclodecapetide, is the first naturally-occurring antibiotic discovered to be selective for sodium and against potassium. Its constitution was established chemically as (IX) (71), which lacks the repetition characteristic of the other macrocyclic antibiotics, and it also differs from them in consisting entirely of L-residues. 

The alkali metal cation complexes of compounds of the valino-mycin group (valinomycin, enniatins, macrotetrolides, beauveridn, antamanide) are positively charged. 

Complex formation constants measured by several groups using various methods are summarized in Table 2 (for full details see (56)). The antibiotics tabulated prefer K+ relative to Na+, except monensin and antamanide, which prefer Na+ relative to K+. These findings are in agreement with ion-selectivity sequences observed in biological systems (6, 57-61). 

A precise calculation of AGd as a function of the cationic radius would be very difficult because it would involve a complete conformational analysis of a large and complicated ligand system (82). Nevertheless, the dependency of the cation selectivity on steric interactions is capable of illustration. The term AGd can be estimated very crudely by using Hooke s law. As is shown in Fig. 16, ligands that are differentiated only by the radius of their equilibrium cavities can easily discriminate between cations of different size. This may explain why valinomycin and antamanide, two antibiotics with similar coordination spheres (54, 66), do not prefer the same cation (82). As it is no easy task to predict the exact dimensions of the cavity for a proposed ligand, the tailored synthesis of such ligands is conceivable yet problematic. 

After the sulfation of alcohols and phenols was reported to proceed efficiently with DCC/ H2S04, 75 76 Wieland et al. 81 applied this procedure for the sulfation of the tyrosine residue in D-Tyr6-a//-D-retro-antamanide. This contains no reactive group in addition to the phenolic group, and the desired product was obtained in satisfactory yields. Despite these promising initial results, this type of sulfation reaction has been adopted only sporadically, e.g. for sulfation of the CCK-8 derivative Boc-Asp(OtBu)-Tyr-Met-Gly-Trp(For)-Met-Asp-(OtBu)-Phe-NH2 with 70% yield1 2 or for the preparation of an intermediate fragment in the synthesis of CCK-related peptides (Scheme 3). 83 ... 

I would like to extend Prof. Simon s characterizations of these beautiful new molecules to include a description of the effects on lipid bilayers of his Na+ selective compound number 11, which my post-doctoral student, Kun-Hung Kuo, and I have found to induce an Na+ selective permeation across lipid bilayer membranes [K.-H. Kuo and G. Eisenman, Naf Selective Permeation of Lipid Bilayers, mediated by a Neutral Ionophore, Abstracts 21st Nat. Biophysical Society meeting (Biophys. J., 17, 212a (1977))]. This is the first example, to my knowledge, of the successful reconstitution of an Na+ selective permeation in an artificial bilayer system. (Presumably the previous failure of such well known lipophilic, Na+ complexing molecules as antamanide, perhydroan-tamanide, or Lehn s cryptates to render bilayers selectively permeable to Na+ is due to kinetic limitations on their rate of complexation and decomplexation). 

Beta structures are found in many small peptides. Tire hormone oxytocin (Fig. 2-4), the antibiotics gramicidin S (Fig. 2-4) and valinomycin (Fig. 8-22), and the mushroom peptide antamanide (Box 28-B) are among these. The cyclic structures of these compounds favor formation of antiparallel (3 strands with sharp turns at the ends. Polypeptide antibiotics that have alternating... 

Because the stability constant of its complex with potassium is much greater than that with sodium, valinomycin is a relatively specific potassium ionophore. In contrast, the mushroom peptide antamanide has a binding cavity of a different geometry and shows a strong preference for sodium ions.388,390 The structure of the Na+-antamanide complex is also shown in Fig. 8-22B. The Streptomyces polyether antibiotic monensin (Fig. 8-22D),389,391 a popular additive to animal feeds, is also an ionophore. However, its mode of action, which involves disruption of Golgi functions, is uncertain 392... 

Figure 8-22 (A) Uncomplexed valinomycin and its complex with K+ (from Duax et al.387). (B) Stereodiagram of the Na-[Phe4, Val6]antamanide complex. A molecule of C2H5OH, which forms the fifth ligand to the Na+, is omitted for clarity. From Karle et al.388 (C) Monensin and its complex with K+. From Pangbom et al.389...

Annelida (segmented worms) 24 Annexins 316,422, 571 Anomeric carbon atom 162 Anomeric effect 166 Antagonists 479 Antamanide 414... 

The same mushrooms contain several fast-acting toxic heptapeptides, the phalloidins, whose structures are similar to those of the amanitins. However, they contain a reduced sulfur atom (—S—) in the cross-bridge. They are specifically toxic to the liver.c The same mushrooms also contain an antidote to the phalloidins, antamanide. This cyclic... 

The amatoxins are cyclic octapeptides composed only of L-amino acids and containing a sulfoxide group instead of the thioether bridge in phallotoxin. Over 90% of the fatal cases of mushroom poisoning can be traced back to the amatoxins. Wieland et al. 234) have shown that, in addition to the toxins, the death cup contains a low concentration of an antitoxic cyclic decapeptide antamanide 108. 

The existence of clathrate-like water structure adjacent to the hydrophobic surfaces of macromolecules is an attractive hypothesis. Models have been proposed which have received some support from thermodynamical arguments [808]. However, this concept has proved ineffective as a basis for the interpretation of the structure associated with the many electron density solvent peaks, separated by 2.8 A to 3.0 A, which are frequently observed on the Fourier X-ray maps close to the surface of a protein [809, 810], Recently, however, some local clathrate-like water has been observed in special cases in the high-resolution studies of the small plant protein, crambin [811], in a hydrated deoxydinucleoside-phosphate drug complex [812], in (Phe4Val6) antamanide hydrate [8131 and in an oligodeoxy-nucleotide duplex [814],... 

Phe4Val6] antamanide 12 H20 X, X All 12 water oxygens located over 16 sites including pentagonal patterns, and bifurcated/three-center bonds [813, 824]... 

Karle IL (1986) Water structure in [Phe4 Ala4] antamanide 12H20 crystallized from diox-ane. Int J Pept Protein Res 28 6-12... 

Karle IL, Duesler E (1977) Arrangement of water molecules in cavities and channels of the lattice of [PheVal6] antamanide dodecahydrate. Proc Natl Acad Sci USA 74 2602 - 2606... 

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