Gramicidin analogues

A. lCBr titration of Enniatin B in methanol. Since exchange of cation between solution and carrier is relatively rapid only one signal is seen per chemically distinct carbonyl. The titration shows the magnitude of the chemical shift observed. Since Enniatin B may be considered a cyclic analogue of Gramicidin A, these chemical shifts indicate the magnitudes of chemical shifts that can be expected in the Gramicidin A channel (see Fig. 6 and 13) for direct interaction of carbonyl with cation. 

Fig.l Chemical structure of the gramicidin S analogue GS-3/3 with 4F-Phg (Fluorine atom is marked red) substituted for Leu3/Leu3 and N-labeled Vall/Vall (Nitrogen atom is marked blue). The peptide is displayed from one hydrophilic surface (A) and from one side (B) to define the molecular axis system used in the structure analysis... 

Amongst the multitude of three-dimensional structures of gramicidin S in the literature [4,32], one asymmetric furanoid sugar-containing analogue indeed forms hexamers with similar intermolecular contacts in the crystal as were derived here in a quasi-native membrane environment [44]. Most... 

J. Xiao, B. Weisbium, P. Wipf, Electrostatic versus steric effects in peptidomimicry Synthesis and secondary structure analysis of gramicidin S analogues with ( )-alkene peptide isosteres, J. Am. Chem. Soc. 127 (2005) 5742-5743. 

A (SCA) 1. HMPPA-pMeBHA (TFA) 2. Nbz-pMeBHA (HF) somatostatin and gramicidin S analogues BOP/HOBt, PyAOP/HOAt Kaiser test yield and purity depends on anchoring Xaa and handle [374]... 

Ripka et al.[167 168l suggested that benzodiazepines of the type 138 (Scheme 52, experimental details given below) could serve as a mimetic of a (3-turn. This mimetic was incorporated into a cyclic octapeptide -containing analogue of the antibiotic peptide gramicidin S to provide 139 (Scheme 53). 

Figure 16.11 Gramicidin S (GS, center), analogue containing hexafluorovalines (left), and analogue containing CF3-(E)-alkene isosteres (right).

An enzyme has been isolated from the FK520 producer which is believed to be the key one responsible for inserting pipecolic acid into the macrocycle [114]. It is reported to be dimeric and activates pipecohc acid and several structural analogues in an ATP-dependent reaction to give an enzyme-bound amino-acyl adenylate. There is evidence that this then reacts to form a thioester linkage to the enzyme. This mechanism of activation is the same as that found in the non-ribosomal biosynthesis of peptide natural products such as gramicidin [112]. 

The structure of gramicidin B and gramiddin C incorporated into SDS micelles has been determined. No significant differences in the backbone of the channel are observed. A comparison of the tryptophan region (i.e. 9 to 15) reveals some small differences in residue orientation that may be of importance in ion binding and transport (Fig. 5). With the Gly-15 analogue of... 

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