The solid phase peptide synthesis introduced in 1%3 by Memfield makes use of an insoluble, functionalized polystyrene support as an inert carrier onto which the amino acid residues are incorporated step by step'). The operational simplicity of this method over the conventional solution phase method has induced intense activity during the last two decades towards a detailed understanding of the physicochemical factors governing the reactions on heterogeneous macromolecular supports. An ideal support for the repetitive synthesis of biopdymers should meet the following requirements: (i) the equivalence of all functional groups as in the case of homogeneous systems, (ii) the physicochemical compatibility of the polymer backbone with the substrates attached to it, and (iii) favourable mechanical properties allowing easy handling which is a prerequisite for automation. These factors control the reactivity and solvation of the bound species and the mass transport of reagents and solvents in polymer-supported reactions2).
Glu(OBzl)]~-~,-Pro-[~-Glu(OBzl)]~ (IX). The oligomers are covalently bound to bifunctional polyethylene glycol (PEG) and monofunctional PEG-M of M , 5 X 103-2 X lo4. Analytical controls were carried out after each step of synthesis in order to ensure quantitative coupling yields. All products could he obtained in high purity as indicated by amino acid analysis, thin-layer chromatography and chiroptical methods. The solubility of the oligomers was strongly enhanced by the presence of the C-terminal PEG group, enabling conformational investigations in a variety of solvents. A significant relationship between conformation and physicochemical properties of the oligopeptides was observed. Oligomers with tendencies to adopt a-helical (1,II) or unordered structures (VI-IX) showed no pronounced change in solubility or coupling kinetics during chain elongation, whereas the onset of a P-structure (IV,V) was paralleled by a drastic decrease in solubility and reactivity of the terminal amino groups. Most notably, the insertion of a proline or glycine in the middle of a P-forming peptide chain (V1,VII) resulted in a considerable increase in solubility compared to the corresponding homo-oligomers. The impact of the conformational properties of a peptide chain on strategic considerations of peptide synthesis in solution is delineated.
Zu einer Losung von 0.56 g (0.75 mmol) (1) in 30 ml Tolu-01 gibt man bei -60 "C 0.095 g (0.75 mmol) (2)['l. Nach 1 h wird das Reaktionsgemisch auf 0 "C gebracht und im Vakuum eingeengt. Der Ruckstand wird in ca. 3 ml Essigester/Dichlormethan (1 : 1) gelost und bei -10 "C an 60 g Aluminiumoxid (Camag, neutral, Aktivitat I) chromatographiert. Mit Hexan werden Olefine, rnit Hexan/Essigester (1 : 1) wird der Komplex (3) eluiert. Die Hauptfraktion wird bei 0 "C im Vakuum eingeengt, der Riickstand kristallisiert aus Ether bei 0°C spontan. Insgesamt erhalt man 0.328 g (52%) (3) als schwach gelbliche Kristalle['"I. Eingegangen dm 8. Juni 1979 [Z 27x1 111 Definition von ,.Bredt-Olefin" und .,Brickenkopf-Olefin" vgl. [3], S. 56X bzw. 528, FuRnote [***I. 121 a) J. Bred(, Ann. Acad. Sci. Fenn. 29, 2. 15 (1927); b) J. R. Wiseman. W. A.Pletcher. J Am. Chem. Soc. 92, 956 (1970). Angew. Chem. 87, 568 (1975); Angew. Chem. Int. Ed. Engl. 14, 52X (1975). 141 a) Fur reversible Stabilisierung eignen sich u. a. auch 12 + 41-Cycioddditio-
Work with peptides can be facilitated by a new protecting group. It combines the structural characteristics and properties of triethylene glycol groups (solubilization) and tert‐butyl groups (acid lability).
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