Synthesis, Characterization, and Cytotoxic Activity of Au^I N,S‐Heterocyclic Carbenes Derived from Peptides Containing L‐Thiazolylalanine

Abstract

Thiazolium salts 2a-b derived from a dipeptide Boc-Gly-(Thz-Ala)-OMe (1b) containing the nonproteinogenic amino acid L-thiazolylalanine (Thz-Ala) can be used to generate the corresponding N,S-heterocyclic carbene (NSHC) gold(I) (3ab) and silver(I) (4) complexes. Reaction of the NSHC-gold(I) iodide 3b with Boc-Cys-Gly-OMe gives access to the peptide bioconjugate 5, which contains a NSHC-Au-(S-Cys) unit. Compounds 3-5 constitute the first coin metal NSHC-peptide complexes. All new compounds were comprehensively characterized by 1 H, 13 C and 2D-NMR spectroscopy, IR spec-[a] 2517 (B) (C β,ThzAla H 2 ), 41.3 (A) and 40.9 (B) [C α,Gly (dip)H 2 ], 36.8 (B) and 30.3 (A) (C β,Cys H 2 ), 28.3 (C Boc H 3 ) and 16.4 (NCH 2 CH 3 ) ppm. HRMS (ESI + ): m/z calcd. for [M + H] + 860.2268; found: 860.2292.Cell Culture: Jurkat (leukaemia) and MiaPaca2 (pancreatic carcinoma) cell lines were maintained in RPMI 1640, whereas A549 (lung carcinoma) cells were grown in DMEM (Dulbecco's Modified Eagle's Medium). Both media were supplemented with 5 % fetal bovine serum (FBS), 200 U/mL penicillin, 100 μg/mL streptomycin, and 2 mm l-glutamine. Media for A549 cells were also supplemented with 2.2 g/l Na 2 CO 3 , 100 μg/mL pyruvate, and 5 mL nonessential amino acids (Invitrogen). Cell cultures were maintained in a humidified atmosphere of 95 % air/5 % CO 2 at 37°C. Cytotoxicity Assay by MTT:The MTT assay was used to determine the cell viability as an indicator for the sensitivity of the cells to the complexes. [44] Exponentially growing cells were seeded at a density of approximately 1 ϫ 10 5 cells/mL (A549, MiaPaca2) or 3 ϫ 10 5 cells/mL (Jurkat), in a 96-well flat-bottomed microplate and, after 24 h, they were incubated with the compounds. The complexes were dissolved in DMSO and tested in concentrations ranging from 0.5 to 100 μm and in quadriplicate. Cells were incubated with the test compounds for 24 h at 37°C, then, 10 μL/well of MTT (5 mg/ mL) was added and plates were incubated for 1-3 h at 37°C. Finally, 100 μL/well iPrOH (0.05 m HCl) was added. The optical density was measured at 570 nm using a 96-well multiscanner autoreader (ELISA). The IC 50 was calculated by nonlinear regression analysis using Origin software (Origin Software, Electronic Arts, Redwood City, California, USA).

Reversible Covalent and Supramolecular Functionalization of Water‐Soluble Gold(I) Complexes

“…The cytotoxicity of complex 4 (IC50=26±2 μ m after 24 h, 38±2 μ m after 48 h and 41±2 μ m after 72 h) is higher than for the positive control cisplatin. This result is consistent with previously disclosed studies for water‐soluble gold(I) phosphane complexes, which reported IC50 values between 1 μ m and 100 μ m , depending on the cell line, incubation time, ligand type and lipophilicity of the gold(I) complexes …”

Synthesis of Gold(I) Derivatives Bearing Alkylated 1,3,5‐Triaza‐7‐phosphaadamantane as Selective Anticancer Metallodrugs

“…In addition, a number of gold conjugates derived from amino acids or peptides have been reported. As examples, N‐heterocyclic carbene (NHC)–gold complexes,, conjugates of ferrocene coordinated to gold(I) derivatives, gold(III) dithiocarbamates,, gold(I) azides, and gold(I) thiolates, with only one example of a chloro–gold–phosphane found in the recent literature.…”

Amino Acids and Peptides as Versatile Ligands in the Synthesis of Antiproliferative Gold Complexes

“…Two gold(I) complexes 50 and 51 with N,S-heterocyclic carbenes derived from the peptides containing l-thiazolylalanine (Thz-Ala) showed good cytotoxic activity in vitro against the A549, MiaPaca2 and Jurkat cell lines (Figure 4a and Table 3) [25]. The carbene complex 50 with iodide was more efficient in all tested cell lines in respect to the thiolate-containing complex 51, what can be the consequence of the higher lability of Au-I bond in respect to the Au-S bond and higher lipophilicity of 50.…”