Treatment of Boc-protected (S)-serine (Ser) methyl ester with triphenylphosphine bromide Ph3PBr (intermittently generated from PPh3 and N-bromosuccinimide) yields Boc-3-bromoalanine (R)-Boc–BrAlaMe and, after deprotection, bromoalanine methyl ester (R)-BrAlaMe in the form of its hydrobromide. Boc–BrAlaMe and BrAlaMe have been structurally characterised. The reaction between BrAlaMe, salicylaldehyde (sal) and VO2+ results in the formation of Schiff base complexes of composition [VO(sal–BrAlaMe)solv]+ (solv = CH3OH: 3, THF: 5) and [VO(sal–BrAla)THF] 4. DFT calculations of the structures of 3, 4 and 5, based on the B3LYP functional and employing the triple zeta basis set 6-311++g(d,p), provide distances Br⋯V = 4.0 ± 0.1 Å, if some distortion of the dihedral angle ∠N–C–C–Br is allowed (affording a maximum energy of ca. 45 kJ mol−1), and thus model Br⋯V distances detected by X-ray methods in bromoperoxidases from the marine algae Ascophyllum nodosum and Corallina pilulifera. The DFT calculations have been validated by comparing calculated and found structures, including the new complex [VVO(Amp–sal)OMe(MeOH)] (1, Amp is the aminophenol moiety) and the known complex [VO(L-Ser–van)H2O] (van = vanillin). Additional validation has been undertaken by checking experimental against calculated (BHandHLYP) EPR spectroscopic hyperfine coupling constants. Complexes containing bromine as a substituent at the phenyl moiety of a Schiff base ligand do not allow for an appropriate simulation of the Br⋯V distance in peroxidases. The closest agreement, d(Br⋯V) = 4.87 Å, is achieved with [VO(3Br–salSer)THF] (6), where 3Brsal–Ser is the dianionic Schiff base formed between 3-Br-5-NO2-salicylaldehyde and serine.
用
三苯基膦溴化物 Ph3PBr(由 PPh3 和 N-
溴代琥珀
酰亚胺间歇性生成)处理 Boc 保护的(S)-
丝氨酸(Ser)甲酯,生成 Boc-3-
溴丙
氨酸(R)-Boc–BrAlaMe,去保护后,形成
溴丙
氨酸甲酯(R)-BrAlaMe 的
氢溴酸盐。 Boc–BrAlaMe 和 BrAlaMe 的结构已被表征。 BrAlaMe、
水杨醛(sal)和 VO2+ 之间的反应形成了化合物 [VO(sal–BrAlaMe)solv]+(solv = CH3OH:3,THF:5)和 [VO(sal–BrAla)THF] 4 的席夫碱配合物。基于 B3LYP 泛函和三重 ζ 基组 6-311++g(d,p) 的 DFT 计算结构,如果允许二面角 ∠N–C–C–Br 有一些扭曲(提供最大能量约为 45 kJ mol−1),则计算出的 Br⋯V 距离为 4.0 ± 0.1 Å,从而模拟了海洋藻类囊褐菌和球状珊瑚菌中
溴过氧化物酶通过 X 射线方法检测到的 Br⋯V 距离。通过比较计算和实际结构,包括新化合物 [VVO(Amp–sal)OMe(MeOH)](1,Amp 是
氨基
酚部分)和已知化合物 [VO(L-Ser–van)H2O](van =
香草醛),验证了 DFT 计算。通过检查实验与计算(BHandHLYP)EPR 光谱超精细耦合常数,进行了额外的验证。含有
溴作为席夫碱
配体中苯部分的取代基的配合物,无法进行
过氧化物酶中 Br⋯V 距离的适当模拟。最接近的一致,d(Br⋯V) = 4.87 Å,是通过 [VO(3Br–salSer)THF](6)实现的,其中 3Brsal–Ser 是由 3-Br-5-
NO2-
水杨醛和
丝氨酸形成的双阴离子席夫碱。