The reactions of α-amino acids and α-amino acid esters with high valent transition metal halides: synthesis of coordination complexes, activation processes and stabilization of α-ammonium acylchloride cations

Abstract

Titanium tetrachloride smoothly reacted with a selection of a-amino acids (aaH) in CH2Cl2 affording yellow\ud to orange solid coordination compounds, 1a–d, in 70–78% yields. The salts [NHEt3][TiCl4(aa)], 2a–b, were\ud obtained from TiCl4/aaH/NEt3 (aa ¼ L-phenylalanine, N,N-dimethylphenylalanine), in 60–65% yields. The\ud complex , 3, was isolated from the reaction of L-proline with\ud NbCl5/NHiPr2, performed in CH2Cl2 at room temperature. The X-ray structure of 3 features a bridging\ud (E)-1,2-bis(3,4-dihydro-2H-pyrrol-5-yl)ethene-1,2-diolate ligand, resulting from the unprecedented C–C\ud coupling between two proline units. Unusually stable a-ammonium acyl chlorides were prepared by the\ud reactions of PCl5/MCln (MCln ¼ NbCl5, WCl6) with L-proline, N,N-dimethylphenylalanine, sarcosine and Lmethionine.\ud MX5 (M ¼ Nb, Ta; X ¼ F, Cl) reacted with L-leucine methylester and L-proline ethylester to\ud give ionic coordination compounds, [MX4L2][MX6] (M ¼ Nb, L ¼ Me2CHCH2CH(NH2)CO2Me, X ¼ F, 9; Cl,\ud 11a; M ¼ Nb, X ¼ Cl, , 11c; Ta, 11d), in moderate to good yields.\ud [NbCl5(Me2CHCH2CHNH3CO2Me)][NbCl6], 12, was isolated as a co-product of the reaction of NbCl5\ud with L-leucine isopropylester, and crystallographically characterized. The reaction of NbCl5 with L-serine\ud isopropylester afforded NbCl3(OCH2CHNHCO2\ud iPr), 13, in 66% yield. The activation of the ester O–R bond\ud was observed in the reactions of L-leucine methyl ester with NbF5 and L-proline ethyl ester with MBr5 (M ¼\ud Nb, Ta), these reactions proceeding with the release of EtF and EtBr, respectively. All the metal products\ud were characterized by analytical and spectroscopic methods, while DFT calculations were carried out in\ud order to provide insight into the structural and mechanistic aspects

Synthesis of Fused Diaziridine Derivatives from Cyclic Secondary Amines by Utilizing N-Bromosulfonamides as an Aminating Reagent

“…New compounds were characterized by 1 H, 13 C, and 19 F NMR spectroscopy, IR spectroscopy, MS, and HRMS. 1 H, 13 Y. Kiyosu et al…”

“…Cyclic secondary amines methyl pyrrolidine-2-carboxylate hydrochloride (1b), 13 2-phenylpyrrolidine, 14 and 1-tosylpiperazine (1i), 15 were prepared according to reported procedures. 1-Pyrroline was prepared according to a reported procedure.…”

“…1 H NMR (CDCl 3 , 400 MHz):  = 7.95 (d, J = 8.0 Hz, 1 H), 7.76-7.67 (m, 2 H), 7.46 (d, J = 8.0 Hz, 1 H), 3.26 (t, J = 5.6 Hz, 4 H), 2.93 (t, J = 5.6 Hz, 4 H). 13…”

“…1 H NMR (CD 3 OD, 400 MHz):  = 7.72 (d, J = 8.4 Hz, 1 H), 7.26 (d, J = 8.4 Hz, 1 H), 2.39 (s, 3 H). 13 C NMR (CD 3 OD, 100 MHz):  = 142. 3, 141.3, 129.7, 128.6, 21.3. Anal.…”

Nanometer‐sized, rod‐like, ligand‐containing tryptophan complexes: Anion influence–structural geometry–antitumor activity correlations

“…[ 8 ] These facts created the need for inhibitors that include other chemical units and for the improvement of selective inhibitors; it was recommended that the use of weaker zinc‐binding groups might be an encouraging approach. [ 9 ] Therefore, metal complex–based proteinogenic α ‐amino acid ligands have become a hot research topic, 10 and the efforts resulted in a wide pharmacological spectrum, including anti‐inflammatory and anticonvulsant properties [ 11 ] in addition to efficient biological and cytotoxic activities. Furthermore, the low production cost and low environmental toxicity of α ‐amino acid complexes [ 12 ] directed efforts for studying metalloprotein systems.…”