单氟烯烃-等排体作为肽骨架的19 F NMR标记:在膜结合的PGLa和(KIGAKI)3中合成和评估。
摘要:
固态19 F NMR是研究生物活性肽与膜相互作用的有力方法。到目前为止,在标记的肽中,19 F-报告基团一直被安装在氨基酸的侧链上。考虑到单氟烯烃是不可水解的肽键模拟物,我们合成了基于单氟烯烃的二肽等位物Val-Ψ[(Z)-CF = CH] -Gly,并将其插入到两个经过充分研究的抗菌素序列中肽:PGLa和(KIGAKI)3是α-螺旋和β-折叠的代表。研究了这些标记肽的构象和生物学活性,以评估一氟烯烃对19 F NMR结构分析的适用性。
单氟烯烃-等排体作为肽骨架的19 F NMR标记:在膜结合的PGLa和(KIGAKI)3中合成和评估。
摘要:
固态19 F NMR是研究生物活性肽与膜相互作用的有力方法。到目前为止,在标记的肽中,19 F-报告基团一直被安装在氨基酸的侧链上。考虑到单氟烯烃是不可水解的肽键模拟物,我们合成了基于单氟烯烃的二肽等位物Val-Ψ[(Z)-CF = CH] -Gly,并将其插入到两个经过充分研究的抗菌素序列中肽:PGLa和(KIGAKI)3是α-螺旋和β-折叠的代表。研究了这些标记肽的构象和生物学活性,以评估一氟烯烃对19 F NMR结构分析的适用性。
stereoselective synthesis of fluoroalkenes was achieved in excellent yields via Pd-catalyzed C-F bond activation. In this transformation, Et3N plays a crucial role to produce reactive hydride species such as Ph(EtO)SiH2 and Ph(EtO)2SiH by promoting dehydrogenative coupling. The reaction proceeds efficiently at 50 degrees C with a variety of substrates and is also useful for the synthesis of fluoroalkene
SmI<sub>2</sub>-Mediated Reduction of γ,γ-Difluoro-α,β-enoates with Application to the Synthesis of Functionalized (<i>Z</i>)-Fluoroalkene-Type Dipeptide Isosteres
A samarium diiodide (SmI2)-mediated reduction of gamma,gamma-difluoro-alpha,beta-enoates (15, 29, and 34) was successfully applied to the synthesis of (Z)-fluoroalkene dipeptide isosteres (23, 30, and 35), which have served as potential dipeptide mimetics. Reduction of the gamma,gamma-difluoro-alpha,beta-enoates by SmI2 proceeded via successive two-electron transfers to form dienolate species which upon kinetically controlled trapping with t-BuOH yielded Xaa-Gly-type fluoroalkene isosteres exemplified by 23, 30, and 35. Replacement of the t-BuOH kinetic trapping agent with aldehydes or ketones provided access to a-substituted fluoroalkene isosteres (43 and 45) through aldol reactions of Sm-dienolates with the carbonyl compounds. Of particular note, the use of the SmI2-HCHO reagent system with chiral enoate 34 provided D-Phe-psi[(Z)-CF=CH]-D/L-Ser isosteres (45), which could be converted to enantiomerically pure isosteres (49-52) that bore a variety of side chain functionalities at the a-position. This was achieved by a sequence of manipulations consisting of beta-lactone formation followed by chromatographic separation and ring-opening with soft nucleophiles. Included in the present work is the first utilization of a Rh-catalyzed Reformatsky reaction of chiral imines for the stereoselective preparation of alpha,alpha-difluoro-beta-amino acid derivatives (28 and 33). The appropriate choice of reagents (carbonyl compounds for kinetic trapping or ring-opening nucleophiles and imines for Reformatsky reactions) allows the presented methodology to yield various fluoroalkene isosteres possessing a wide range of side chain functionalities.