Cyclic oligopeptides

Beyond the relatively rigid cyclic dipeptides (dioxopiperazines see Chapter 6), macrocyclic peptides show considerable flexibility though relatively less flexibility than that of their acyclic analogues. The biological importance of cyclic peptides has 

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Chemical Name Cyclic oligopeptide (See Structural Formula)... 

Library of Cyclic Oligopeptides as Additives to Background Electrolyte for Chiral Capillary Electrophoresis... 

A separation of myoglobin and lysozyme has been presented by Nicoud [44]. This purification was performed on SMB containing 8 columns using ACA 54 (Biosepra, France) as support. Very pure extracts (>98%) and raffinates (>98%) were obtained from a 50-50 mixture. An internal profile is given in Fig. 7. Another recently presented example is the separation of cyclosporine A from cyclic oligopeptide and other impurities in the reversed phase mode or by adsorption on silica gel presented by Schulte et al. [10]. 

Crown ethers and cyclic oligopeptides are also accessible by this method (Schemes 9.2 and 9.3). Thus, C-unprotected di- and tri-peptides activated by the... 

Quantitative analysis and prediction of hydrophoby of cyclic oligopeptides 91YGK836. 

A cyclic oligopeptide-containing azobenzene unit A-12 took a (3-tum-like structure after UV irradiation, while it was rather an extended structure before irradiation, as elucidated by NMR and molecular dynamics calculations [83]. ... 

Alternative chemical strategies for the synthesis of nanomaterials, like the organization in the critical region, also rely on self-assembly of suitable monomers. Cyclic oligopeptides may, for instance, be synthesized by linking eight amino acid residues by covalent bonds. The resulting macrocycles self-assemble into nanoscaled tube-like arrays. 

Figure 37 Electron micrographs of self-assembled fibres, (c) Electron micrograph showing the dense network of long helical fibres in a steroid/cyclohexane organogel, (d) Preparation of single fibres, demonstrating their helical superstructure [425]. (e) Cyclic oligopeptides, selfassembling into nanofibres [435,436], Reproduced with permission of The Royal Society of Chemistry and The American Chemical Society. Parts (c) and (d) 1986 American Chemical Society...

As mentioned above, some naturally occurring cyclic hosts that possess molecular recognition capabilities were known before crown ethers (the first artificial host molecules) were discovered. For example, the cyclic oligopeptide valinomycin and the cyclic oligosaccharide cyclodextrin were found to bind to specific guest molecules. The chemical modification of cyclodextrin was particularly well-researched, and artificially modified cyclodextrins became one of the most important compoimds used in host-guest chemistry. 

This problem is most pronounced in aerobic fungi while green plants which spend some N (in amino acids) to obtain metals, do so usually in well-aerated or at least nitrate-containing soils. Further apart from green plants in terms of taxonomy, this problem also exists with Ee(III) reducers which have C/N >100 but employ cyclic oligopeptides and sometimes also hydrox-amates to mobilize Ee(III) from solid oxides. The limits which then are upper limits for C/N ratios are given for a number of different organisms (Table 2.21) ... 

Production of cyclic oligopeptides as secondary metabolites by freshwater cyanobacteria 04CPB889. 

Distance Geometry Algorithm to Cyclic Oligopeptide Conformation Searches. 

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