Mass spectrometric studies on 17β-estradiol-17-fatty acid esters: Evidence for the formation of anion-dipole intermediates
摘要:
AbstractThe behaviour towards low collision energy processes (eV range) of [M H]− prepared under negative ion chemical ionization (NICI) ammonia conditions from 17β‐estradiol‐17‐fatty acid esters has been investigated. From such bifunctional compounds containing two acidic sites (i.e. phenol and ester groups), two isomeric forms (i.e. phenoxide and enolate forms) characterize the [M H]− ion structures, whose distribution depends on the ion preparation mode. Here NICI (ammonia) provides both phenoxide and enolate forms as the [M H]− species. This behaviour contrasts with the regioselectivity observed for proton abstraction from phenol under NICI (N2O) and fast atom bombardment conditions. Production of both phenoxide and enolate forms in NICI (ammonia) is demonstrated under NICI (ND3) conditions in which DO‐labelled [Md H]− enolate ions are produced in a similar yield to unlabelled [Md D]− phenoxide ions. Collisionally activated dissociation (CAD) spectra of both isomeric deprotonated molecules differ strongly by the presence of two different pairs of complementary daughter ions, suggesting that these ionic species are unconvertible. This is due to a steric hindrance effect on the long‐distance proton transfer. A mechanistic investigation on the formation of fragment ion pairs produced under CAD was performed with various deuterium‐labelled molecules. From these experiments, evidence is provided for molecular isomerizations into ion‐dipole complexes (prior to dissociation) which are structurally dependent on the initial charge location. Direct dissociation of these intermediates competes with the occurrence of exothermic proton transfer(s) yielding the formation of other isomeric intermediate forms. The orientation of these proton transfers is dictated by the relative acidities of both moieties of the complex.
Pentafluorophenyl Esters: Highly Chemoselective Ketyl Precursors for the Synthesis of α,α-Dideuterio Alcohols Using SmI<sub>2</sub> and D<sub>2</sub>O as a Deuterium Source
作者:Hengzhao Li、Yuxia Hou、Chengwei Liu、Zemin Lai、Lei Ning、Roman Szostak、Michal Szostak、Jie An
DOI:10.1021/acs.orglett.9b04383
日期:2020.2.21
We report the first highly chemoselective synthesis of α,α-dideuterio alcohols with exquisite incorporation of deuterium (>98% [D2]) using pentafluorophenyl esters as ketyl radical precursors, SmI2 as a mild reducing agent, and D2O as the deuterium source. This system tolerates a variety of functional groups, offering rapid entry to valuable α,α-dideuterated alcohol building blocks. More generally
A highly chemoselective reductive deuteration of acylfluorides to provide α,α-dideuterio alcohols with exquisite levels of deuterium incorporation was developed using SmI2 and D2O as the deuterium source. This method introduces acylfluorides as attractive radical precursors for the generation of reactive acyl-type fluoride ketyls that should find widespread application in many synthetic strategies
作者:A. Firouzi、F. Atef、A. G. Oertli、G. D. Stucky、B. F. Chmelka
DOI:10.1021/ja963007i
日期:1997.4.1
of a basic aqueous solution containing anionic silicate oligomers (e.g., double-four-ring species) to an isotropic micellar solution of cationic surfactant molecules (e.g., cetyltrimethylammonium bromide). Important similarities and differences are shown to exist between multicomponent silicate−surfactant and conventional binary lyotropic liquid crystals. Under highly alkaline conditions, the silicate−surfactant
多核 (2H, 13C, 29Si, 81Br) 磁共振光谱、小角 X 射线散射和偏振光学显微镜技术已被用于研究具有六方和层状形态的硅酸盐 - 表面活性剂溶致液晶中的分子和介观组织。碱性条件。在将包含阴离子硅酸盐低聚物(例如,双四环物质)的碱性水溶液添加到阳离子表面活性剂分子(例如,十六烷基三甲基溴化铵)的各向同性胶束溶液中之后,此类系统协同自组装。多组分硅酸盐表面活性剂和传统的二元溶致液晶之间显示出重要的相似性和差异。在强碱性条件下,