Efficient Decarboxylative/Defluorinative Alkylation for the Synthesis of
<scp>
<i>gem</i>
‐Difluoroalkenes
</scp>
through an
<scp>
S
<sub>N</sub>
2
</scp>
’‐Type Route
作者:Wei‐Long Xing、Jia‐Xin Wang、Ming‐Chen Fu、Yao Fu
DOI:10.1002/cjoc.202100709
日期:2022.2
An efficientdecarboxylative/defluorinativealkylation for synthesizing gem-difluoroalkenes is described, providing a general method for installation of the challenging alkyl fragments containing α-electron-withdrawing groups into α-trifluoromethyl alkenes. Mechanistic studies suggest that this process involves an SN2′-type synthetic route in the absence of transition-metal catalysts or photocatalysis
描述了一种用于合成偕二氟烯烃的有效脱羧/脱氟烷基化反应,为将含有 α-吸电子基团的具有挑战性的烷基片段安装到 α-三氟甲基烯烃中提供了一种通用方法。机理研究表明,该过程涉及在没有过渡金属催化剂或光催化的情况下的 S N 2' 型合成路线。此外,该协议可以很容易地扩大规模,并成功应用于生物活性分子的修饰,从而补充了获得结构通用的gem-二氟烯烃的方法。
Synthesis and Physicochemical Characterization of Carbon Backbone Modified [Gd(TTDA)(H<sub>2</sub>O)]<sup>2−</sup> Derivatives
作者:Ya-Hui Chang、Chiao-Yun Chen、Gyan Singh、Hsing-Yin Chen、Gin-Chung Liu、Yih-Gang Goan、Silvio Aime、Yun-Ming Wang
DOI:10.1021/ic101799c
日期:2011.2.21
The present study was designed to exploit optimum lipophilicity and high water-exchange rate (k(ex)) on low molecular weight Gd(III) complexs to generate high bound relaxivity (r(1)(b)), upon binding to the lipophilic site of human serum albumin (HSA). Two new carbon backbone modified TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid) derivatives, CB-TTDA and Bz-CB-TTDA, were synthesized. The complexes [Gd(CB-TTDA)(H2O)](2-) and [Gd(Bz-CB-TTDA)(H2O)](2-) both display high stability constant (log K-GdL = 20.28 and 20.09, respectively). Furthermore, CB-TTDA (log K-(Gd/Zn) = 4.22) and Bz-CB-TTDA (log K-(Gd/Zn) = 4.12) exhibit superior selectivity of Gd(III) against Zn(II) than those of TTDA (log K-(Gd/Zn) = 2.93), EPTPA-bz-NO2 (log K-(Gd/Zn) = 3.19), and DTPA (log K-(Gd/Zn) = 3.76). However, the stability constant values of [Gd(CB-TTDA)(H2O)](2-) and [Gd(Bz-CB-TTDA)(H2O)](2-) are lower than that of MS-325. The parameters that affect proton relaxivity have been determined in a combined variable temperature O-17 NMR and NMRD study. The water exchange rates are comparable for the two complexes, 232 x 10(6) s(-1) for [Gd(CB-TTDA)(H2O)](2-) and 271 x 10(6) s(-1) for [Gd(Bz-CB-TTDA)(H2O)](2-). They are higher than those of [Gd(TTDA)(H2O)](2-) (146 x 10(6) s(-1)), [Gd(DTPA)(H2O)](2-) (4.1 x 10(6) s(-1)), and MS-325 (6.1 x 10(6) s(-1)). Elevated stability and water exchange rate indicate that the presence of cyclobutyl on the carbon backbone imparts rigidity and steric constraint to [Gd(CB-TTDA)(H2O)](2-) and [Gd(Bz-CB-TTDA)(H2O)](2-). In addition, the major objective for selecting the cyclobutyl is to tune the lipophilicity of [Gd(Bz-CB-TTDA)(H2O)](2-). The binding affinity of [Gd(Bz-CB-TTDA)(H2O)](2-) to HSA was evaluated by ultrafiltration study across a membrane with a 30 kDa MW cutoff, and the first three stepwise binding constants were determined by fitting the data to a stoichiometric model. The binding association constants (K-A) for [Gd(CB-TTDA)(H2O)](2-) and [Gd(Bz-CB-TTDA)(H2O)](2-) are 1.1 x 10(2) and 1.5 x 10(3), respectively. Although the K-A value for [Gd(Bz-CB-TTDA)(H2O)](2-) is lower than that of MS-325 (K-A = 3.0 x 10(4)), the r(1)(b) value, r(1)(b) = 66.7 mM(-1) s(-1) for [Gd(Bz-CB-TTDA)(H2O)](2-), is significantly higher than that of MS-325 (r(1)(b) = 47.0 mM(-1) s(-1)). As measured by the Zn(II) transmetalation process, the kinetic stabilities of [Gd(CB-TTDA)(H2O)](2-), [Gd(Bz-CB-TTDA)(H2O)](2-), and [Gd(DTPA)(H2O)](2-) are similar and are significantly higher than that of [Gd(DTPA-BMA)(H2O)](2-) High thermodynamic and kinetic stability and optimized lipophilicity of [Gd(CB-TTDA)(H2O)](2-) make it a favorable blood pool contrast agent for MRI.
Preparation and Structure ofβ-Peptides Consisting of Geminally Disubstitutedβ2,2- andβ3,3-Amino Acids: A Turn Motif forβ-Peptides
We report on the synthesis of new and previously described beta-peptides (1-6), consisting of up to twelve beta(2,2-) or beta(3,3)-geminally disubstituted beta-amino acids which do not fit into any of the secondary structural patterns of beta-peptides, hitherto disclosed. The required 2,2- and 3,3-dimethyl derivatives of 3-aminopropanoic acid are readily obtained from 3-methylbut-2-enoic acid and ammonia (Scheme 1) and from Boc-protected methyl 3-aminopropanoate by enolate methylation (Scheme 2). Protected (Boc for solution-, Fmoc for solid-phase syntheses) 1-(aminomethyl)cycloalkanecarboxylic-acid derivatives (with cyclopropane, cyclobutane, cyclopentane, and cyclohexane rings) are obtained from 1-cyanocycloalkanecarboxylates and the corresponding dihaloalkanes (Scheme 3). Fully C-13- and N-15-labeled 3-amino-2,2-dimethylpropanoic-acid derivatives were prepared from the corresponding labeled precursors (see asterixed formula numbers and Scheme 4). Coupling of these amino acids was achieved by methods which we had previously employed for other beta-peptide syntheses ( intermediates 18 - 23). Crystal structures of Boc-protected geminally disubstituted amine acids (16a-d) and of the corresponding tripeptide (23a), as well as NMR and IR spectra of an isotopically labeled beta-hexapeptide (2a*) are presented (Figs. 1-4) and discussed. The tripeptide structure contains a ten-membered H-bonded ring which is proposed to be a turn-forming motif for beta-peptides (Fig. 2).
Oediger,H.; Moeller,F., Justus Liebigs Annalen der Chemie, 1976, p. 348 - 351