Khaled M A, Davies D B
Biochim Biophys Acta. 1982 Jun 4;704(2):186-96. doi: 10.1016/0167-4838(82)90145-5.
The conformational properties of the cyclohexadepsipeptide antibiotic Beauvericin have been investigated by 1H-NMR spectroscopy in polar (C2H3O2H) and non-polar (CCl4, C62H6, C2HCl3) solvents and in two solvent mixtures; one a mixture of a polar and non-polar solvent (C2H3O2H/CCl4) and the other an aromatic solvent in a non-polar environment (C62H6/CCl4). The ion-complexation properties of Beauvericin with alkali metal halides (Li+, Na+, K+, Cs+) have also been studied. It is demonstrated that changes in chemical shifts of Beauvericin with concentration, with polarity of solvent or with added alkali metal ion reflect changes not only in the solvent properties but also changes in backbone conformation and changes due to ion-complexation, where appropriate, and therefore cannot be used, by themselves, to determine the conformation of the molecule, its self-aggregation properties, or the stoichiometry of the metal ion-complex. The backbone conformations of Beauvericin in different environments are determined by methods that are independent of chemical shift analysis; i.e., by measurements of 5J(HH) magnitudes observed between the alpha-CH protons of the L-phenylalanine and D-hydroxyisovaleric acid (DHyIv) residues and by nuclear Overhauser effect measurements observed between alpha-CH(HyIv) and (N)-CH3(Phe) proton signals. In the knowledge of these results the chemical shifts of Beauvericin in different environments can then be rationalised. It is found that the conformation of Beauvericin in a polar solvent is different from that found in a non-polar solvent and from that found for the in the ion-complexed form is similar to that found in non-polar solvents. By taking into account the conformational properties of the L-phenylalanine and DHyIv side-chains, it is possible to assign unambiguously the magnetically non-equivalent beta-CH2(Phe) and gamma Me(HyIv) proton signals and so elucidate the complete conformational behaviour of the uncomplexed forms of Beauvericin in a polar and a non-polar environment, and of the ion-complexed form of Beauvericin in a polar solvent.
通过1H-NMR光谱，在极性（乙酸，C2H3O2H）和非极性（四氯化碳CCl4、苯C62H6、三氯乙烷C2HCl3）溶剂以及两种溶剂混合物中研究了环六肽抗生素白僵菌素的构象性质；一种是极性和非极性溶剂的混合物（乙酸/四氯化碳，C2H3O2H/CCl4），另一种是在非极性环境中的芳香族溶剂（苯/四氯化碳，C62H6/CCl4）。还研究了白僵菌素与碱金属卤化物（Li+、Na+、K+、Cs+）的离子络合性质。结果表明，白僵菌素的化学位移随浓度、溶剂极性或添加的碱金属离子的变化，不仅反映了溶剂性质的变化，还反映了主链构象的变化以及在适当情况下由于离子络合引起的变化，因此，仅凭这些变化本身不能用于确定分子的构象、其自聚集性质或金属离子络合物的化学计量。白僵菌素在不同环境中的主链构象是通过与化学位移分析无关的方法确定的；即通过测量L-苯丙氨酸和D-羟基异戊酸（DHyIv）残基的α-CH质子之间观察到的5J(HH)大小，以及通过观察α-CH(HyIv)和(N)-CH3(Phe)质子信号之间的核Overhauser效应来确定。根据这些结果，然后可以合理解释白僵菌素在不同环境中的化学位移。发现白僵菌素在极性溶剂中的构象与在非极性溶剂中的构象不同，并且其离子络合形式的构象与在非极性溶剂中发现的构象相似。通过考虑L-苯丙氨酸和DHyIv侧链的构象性质，可以明确指定磁性不等价的β-CH2(Phe)和γ Me(HyIv)质子信号，从而阐明白僵菌素在极性和非极性环境中的未络合形式以及在极性溶剂中的离子络合形式的完整构象行为。
