Synthesis and Antioxidant Evaluation of O-Methylated Emodacidamides: Starting from Parietin, a Secondary Metabolite of Lichen Xanthoria parietina.

Polyhydroxy-anthraquinones bearing amino acids are found rather seldom in nature. Emodacidamides, isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101 by Luo et al. (2017) are the first natural example of amino acid conjugated anthraquinone. In this study, O-methylated emodacidamides and emodinic acid-anilides were synthesized starting from parietin, extracted from the lichen Xanthoria parietina (L.) Th. Fr. The structural elucidations of prepared compounds were confirmed by 1D and 2D NMR analyses including HSQC and HMBC techniques. In addition, all newly synthesized compounds were evaluated for the antioxidant activities with free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The synthesized compounds showed low to moderate antioxidant and DPPH scavenging activities. The antioxidant activities were supported within quantum chemical calculations using the DFT-B3LYP/6-311++G(d,p) level of theory. It is observed that the antioxidant activity of emodacidamides mostly depends on the phenolic groups on anthraquinone ring. The phenolic groups on other substituents help to improve antioxidant activity and also the position of hydroxy group is a decisive factor for antioxidant ability.

Cytotoxic, apoptotic and cell migration inhibitory effects of atranorin on SPC212 mesothelioma cells

Objective: To investigate the effects of atranorin, a lichen secondary metabolite, on SPC212 malignant mesothelioma cells in vitro. Methods: SPC212 malignant mesothelioma cell line was used. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to evaluate cytotoxic effects of atranorin and cisplatin at 24, 48 and 72 h. Hematoxylin-eosin staining and 4',6-diamidino-2-phenylindole, dihydrochloride staining were used for determining cell and nucleus morphology, respectively. Wound healing assay was used for investigating cell migration. The xCELLigence real-time cell analysis system was used for determining cell proliferation. Results: Atranorin at 5-450 μM decreased cell viability at 24, 48 and 72 h. IC50 values of atranorin were 300.94, 292.6 and 278.02 μM at 24, 48 and 72 h, respectively; meanwhile, the IC50 values of cisplatin were 128.00, 34.37 and 17.05 μM at 24, 48 and 72 h, respectively. Furthermore, atranorin disrupted cell and nuclear morphology with increasing concentrations. Atranorin significantly reduced cell migration by 38%, 37% and 35% at 300, 250 and 200 μM, respectively (P＜0.000). Atranorin at 160-450 μM decreased cell proliferation at 72 h (P＜0.000). Conclusions: Atranorin has cytotoxic, antiproliferative, apoptotic and cell migration inhibitory effects on SPC212 malignant mesothelioma cancer cells.

Peptidomimetics via modifications of amino acids and peptide bonds.

Peptidomimetics represent an important field in chemistry, pharmacology and material science as they circumvent the limitations of traditional peptides used in therapy. Self-structural organizations such as turns, helices, sheets and loops can be accessed by chemical modifications of amino acids or peptides. In-depth structural and conformational analysis and structure-activity relationships (SAR) offer a way to establish peptidomimetic libraries. Herein, we review recent developments in peptidomimetics that are formed via heteroatom replacement within the native amino acid backbone. Each sub-section describes structural features, utility and preparative methods.

Photophysics of novel coumarin-labeled depsipeptides in solution: sensing interactions with SDS micelle via TICT model.

N-Acylbenzotriazoles enable the synthesis (69-92% yield) of blue to green fluorescent coumarin-labeled depsidipeptides 8a-f (quantum yields 0.004-0.97) and depsitripeptides 12a-d (quantum yields 0.02-0.96). Detailed photophysical studies of fluorescent coumarin-labeled depsipeptides 8a-f and 12a-d are reported for both polar protic and polar aprotic solvents. 7-Methoxy and 7-diethylaminocoumarin-3-ylcarbonyl depsipeptides 8c,f and 12d are highly solvent sensitive. These highly fluorescent compounds could be useful for peptide assays. Further photophysical studies of 7-diethylaminocoumarin-labeled depsipeptides 8c,12d within the micellar microenvironment of SDS reflect their ability to bind with the biological membrane, suggesting potential applications in the fields of bio- and medicinal chemistry.

Benzotriazole-mediated synthesis of aza-peptides: en route to an aza-leuenkephalin analogue.

Novel N-(N-Pg-azadipeptidoyl)benzotriazoles 20a-e couple efficiently with α-amino acids 21a-e, dipeptides 22a-c, aminoxyacetic acid 23a, depsidipeptide 23b, and α-hydroxy-ß-phenylpropionic acid 27 yielding, respectively, azatripeptides 24a-g, azatetrapeptides 25a,b, a hybrid azatripeptide with an oxyamide bond 26a, a hybrid azatetrapeptide with an ester bond 26b, and a hybrid azatripeptide with an ester bond 28. A new protocol for the synthesis of N-Pg-azatripeptides 33a,b and 35a,b, each containing a natural amino acid at the N-terminus, avoids the low coupling rates of the aza-amino acid residue and enables the solution-phase synthesis of an azaphenylalanine analogue of Leu-enkephalin 40.

Design, synthesis, and biological activity of a novel series of 2,5-disubstituted furans/pyrroles as HIV-1 fusion inhibitors targeting gp41.

Based on molecular docking analysis of earlier results, we designed a series of 2,5-disubstituted furans/pyrroles (5a-h) as HIV-1 entry inhibitors. Compounds were synthesized by Suzuki-Miyaura cross coupling, followed by a Knoevenagel condensation or Wittig reaction. Four of these compounds were found to be effective in inhibiting HIV-1 infection, with the best compounds being 5f and 5h, which exhibited significant inhibition on HIV-1(IIIB) infection at micromolar levels with low cytotoxicity. These compounds are also effective in blocking HIV-1 mediated cell-cell fusion and the gp41 six-helix bundle formation, suggesting that they are also HIV-1 fusion inhibitors targeting gp41 and have potential to be developed as a new class of anti-HIV-1 agents.

Benzotriazole-mediated syntheses of depsipeptides and oligoesters.

Reactions of O-Pg(α-hydroxyacyl)benzotriazoles with (a) unprotected α-hydroxycarboxylic acids, (b) amino acids, and (c) amines afforded, respectively, chirally pure (a) oligoesters, (b) depsidipeptides, and (c) amide conjugates (yields 52-94%). N-Pg(α-Aminoacyl)benzotriazoles reacted with α-hydroxycarboxylic acids to yield depsidipeptides (47-87%). N-Pg(depsidipeptidoyl)benzotriazoles, obtained from depsidipeptides, gave depsitripeptides (yields 55-78%) on reaction with amino acids and α-hydroxycarboxylic acids. O-Acylation of α-hydroxycarboxylic acids with N-Pg(α-aminoacyl)benzotriazoles followed by deprotection produced unprotected depsides useful for the preparation of depsitripeptides.

Design, synthesis, and biological activity of novel 5-((arylfuran/1H-pyrrol-2-yl)methylene)-2-thioxo-3-(3-(trifluoromethyl)phenyl)thiazolidin-4-ones as HIV-1 fusion inhibitors targeting gp41.

On the basis of our earlier molecular docking analysis, we designed and synthesized 5-((arylfuran/1H-pyrrol-2-yl)methylene)-2-thioxo-3-(3-(trifluoromethyl)phenyl)thiazolidin-4-ones (12a-o) as HIV-1 entry inhibitors. Compounds 12a-o effectively inhibited infection by both laboratory-adapted and primary HIV-1 strains and blocked HIV-1 mediated cell-cell fusion and gp41 six-helix bundle formation. Molecular docking analyses on two highly active inhibitors, 12b, containing a carboxylic acid group, and 12m, containing a tetrazole group, indicated that they both fit snugly into the hydrophobic cavity of HIV-1 gp41 from which each has important ionic interactions with lysine 574 (K574). By contrast, molecular docking of 12i, a less active compound containing a pyrrole instead of a furan ring, indicated a completely different orientation from 12b and 12m and missed critical interactions.

Efficient preparation of aminoxyacyl amides, aminoxy hybrid peptides, and alpha-aminoxy peptides.

N-(Pg-alpha-aminoxy acids) 1a-g are converted to N-(Pg-alpha-aminoxyacyl)benzotriazoles 2a-g, which react under mild conditions with amines, alpha-amino acids/alpha-dipeptides, and alpha-aminoxy acids to give aminoxyacyl amides 3a-g, (3e+3e'), and (3g+3g'), aminoxy hybrid peptides 4a-h, (4a+4a'), 6a-d, 9a-e, (9a+9a'), and (9b+9b'), and alpha-aminoxy peptides 10a,b in good yields without racemization.