Tiered approach for evaluation of anti-melanogenic activity of trans-N-coumaroyltyramine derivatives.

Skin hyperpigmentation is commonly treated by topical drug application. Several naturally occurring compounds exhibit attractive biological effects including anti-melanogenic activity. Chemically modified derivatives of those compounds are expected to be more efficient. However, efficacy and safety testing processes are of significant consideration to identify the most effective compound among them. Herein, we demonstrated a tiered approach to investigate the antipigmentation activity of 17 trans-N-coumaroyltyramine derivatives. First, we evaluated the in chemico antityrosinase activity, then the cytotoxicity of the most potent derivatives using a mitochondrial activity-based assay, followed with the in vitro anti-melanogenic activity in two dimensional (2D) monolayer human melanocytes. The selected derivatives were topically applied on a three dimensional (3D) pigmented-reconstructed human epidermis (pRhE) containing melanocytes and keratinocytes to evaluate their depigmenting activity. Two of the 17 derivatives displayed a significant reduction in pigmentation in the 3D pRhE, comparable to kojic acid, a known tyrosinase inhibitor. In addition, a molecular docking experiment indicated an interaction of the three derivatives and tyrosinase, suggesting that these derivatives have potent anti-melanogenic activity through tyrosinase inhibition. Our findings provide an alternative approach for investigating skin-whitening agents, thereby facilitating the research and development of skin-whitening products that need not be tested on animals.

Pyrrolidinyl peptide nucleic acids bearing hydroxy-modified cyclobutane building blocks: Synthesis and binding properties.

The conformationally constrained pyrrolidinyl PNA with a dipeptide consisting of an alternating nucleobase-modified D-proline and a cyclic ß-amino acid "spacer" exhibited improved nucleic acid binding properties compared to the original PNA. The pyrrolidinyl PNA with the four-membered ring spacer (1S,2S)-2-aminocyclobutanecarboxylic acid (acbcPNA) are among the best performed members of the pyrrolidinyl PNA family. However, these PNA suffer some limitations such as aqueous solubility and non-specific interactions due to their extreme hydrophobicity. In the present work, a hydroxy group is introduced onto the cyclobutane ring spacer of the acbcPNA with the aim of decreasing its hydrophobicity. To this end, a Fmoc/tBu ether-protected 4-hydroxy-2-aminocyclobutanecarboxylic acid building block was synthesized and resolved by chiral HPLC. Each enantiomer was used to synthesize the hydroxy-modified acbcPNA employing Fmoc solid-phase peptide synthesis. DNA/RNA binding studies indicated that the introduction of the hydroxy group to the acbcPNA decreases the binding affinity toward complementary DNA and RNA while maintaining the sequence and directional specificity of unmodified acbcPNA. The hydrophobicity of the hydroxy-modified acbcPNA decreased with the number of hydroxy groups added as indicated by the decrease in the logP values. Only two modifications were sufficient to decrease the logP by an order of magnitude without excessively lowering the binding affinity nor the specificity. This work thus demonstrated that the specific structural modifications for this type of PNA model can be performed in a modular fashion, which paves the way toward the future realization of improving hydrophilicity and nucleic acid binding affinity as well as specificity.

ß-Keto and ß-hydroxyphosphonate analogs of biotin-5'-AMP are inhibitors of holocarboxylase synthetase.

Holocarboxylase synthetase (HLCS) catalyzes the covalent attachment of biotin to cytoplasmic and mitochondrial carboxylases, nuclear histones, and over a hundred human proteins. Nonhydrolyzable ketophosphonate (ß-ketoP) and hydroxyphosphonate (ß-hydroxyP) analogs of biotin-5'-AMP inhibit holocarboxylase synthetase (HLCS) with IC50 values of 39.7 µM and 203.7 µM. By comparison, an IC50 value of 7 µM was observed with the previously reported biotinol-5'-AMP. The Ki values, 3.4 µM and 17.3 µM, respectively, are consistent with the IC50 results, and close to the Ki obtained for biotinol-5'-AMP (7 µM). The ß-ketoP and ß-hydroxyP molecules are competitive inhibitors of HLCS while biotinol-5'-AMP inhibited HLCS by a mixed mechanism.

Re2O7-catalyzed reaction of hemiacetals and aldehydes with O-, S-, and C-nucleophiles.

Re(VII) oxides catalyze the acetalization, monoperoxyacetalization, monothioacetalization and allylation of hemiacetals. The reactions, which take place under mild conditions and at low catalyst loadings, can be conducted using hemiacetals, the corresponding O-silyl ethers, and, in some cases, the acetal dimers. Aldehydes react under similar conditions to furnish good yields of dithioacetals. Reactions of hemiacetals with nitrogen nucleophiles are unsuccessful. 1,2-Dioxolan-3-ols (peroxyhemiacetals) undergo Re(VII)-promoted etherification but not allylation. Hydroperoxyacetals (1-alkoxyhydroperoxides) undergo selective exchange of the alkoxide group in the presence of either Re2O7 or a Brønsted acid.

In vitro and in vivo activity of 3-alkoxy-1,2-dioxolanes against Schistosoma mansoni.

OBJECTIVES: Compounds characterized by a peroxidic skeleton are an interesting starting point for antischistosomal drug discovery. Previously a series of 3-alkoxy-1,2-dioxolanes, which are chemically stable cyclic peroxides, demonstrated significant in vitro activity against Plasmodium falciparum. We aimed to evaluate the potential of these compounds against Schistosoma mansoni and elucidate the roles of iron and peroxidic groups in activity. METHODS: Drugs were tested against juvenile and adult stages of S. mansoni in vitro and in vivo. Selected structures were assessed in vitro against schistosomes in the presence of additional iron sources. In addition, drugs were tested in vitro and in vivo against Echinostoma caproni, a non-blood-feeding intestinal fluke. Finally, the activity of non-peroxidic analogues was evaluated. RESULTS: Three dioxolanes displayed IC50s ≤ 20.1 µM against adult schistosomes and values as low as 4.2 µM against newly transformed schistosomula. Nonetheless, only moderate, non-significant worm burden reductions were observed after treatment of mice harbouring adult infections. Drugs lacked activity against juvenile schistosomes in vivo. Two selected dioxolanes showed in vitro activity against E. caproni down to concentrations of 5 mg/L, but none of the compounds revealed in vivo activity. All tested non-peroxidic analogues lacked activity in vitro against both parasites. CONCLUSIONS: Selected dioxolanes presented interesting in vitro activity, but low in vivo activities have to be overcome to identify a lead candidate. Although the inactivity of non-peroxidic analogues underlines the necessity of a peroxide functional group, incubation of adult schistosomes with additional iron sources did not alter activity, supporting an iron-independent mode of activation.

Novel Amphiphilic Cyclobutene and Cyclobutane cis-C18 Fatty Acid Derivatives Inhibit Mycobacterium avium subsp. paratuberculosis Growth.

Mycobacterium avium subspecies paratuberculosis (Map) is the etiologic agent of Johne's disease in ruminants and has been associated with Crohn's disease in humans. An effective control of Map by either vaccines or chemoprophylaxis is a paramount need for veterinary and possibly human medicine. Given the importance of fatty acids in the biosynthesis of mycolic acids and the mycobacterial cell wall, we tested novel amphiphilic C10 and C18 cyclobutene and cyclobutane fatty acid derivatives for Map inhibition. Microdilution minimal inhibitory concentrations (MIC) with 5 or 7 week endpoints were measured in Middlebrook 7H9 base broth media. We compared the Map MIC results with those obtained previously with Mycobacterium tuberculosis and Mycobacterium smegmatis. Several of the C18 compounds showed moderate efficacy (MICs 392 to 824 µM) against Map, while a higher level of inhibition (MICs 6 to 82 µM) was observed for M. tuberculosis for select analogs from both the C10 and C18 groups. For most of these analogs tested in M. smegmatis, their efficacy decreased in the presence of bovine or human serum albumin. Compound 5 (OA-CB, 1-(octanoic acid-8-yl)-2-octylcyclobutene) was identified as the best chemical lead against Map, which suggests derivatives with better pharmacodynamics may be of interest for evaluation in animal models.

Development of cyclobutene- and cyclobutane-functionalized fatty acids with inhibitory activity against Mycobacterium tuberculosis.

Eleven fatty acid analogues incorporating four-membered carbocycles (cyclobutenes, cyclobutanes, cyclobutanones, and cyclobutanols) were investigated for the ability to inhibit the growth of Mycobacterium smegmatis (Msm) and Mycobacterium tuberculosis (Mtb). A number of the analogues displayed inhibitory activity against both mycobacterial species in minimal media. Several of the molecules displayed potent levels of inhibition against Mtb, with MIC values equal to or below those observed with the anti-tuberculosis drugs D-cycloserine and isoniazid. In contrast, two of the analogues that display the greatest activity against Mtb failed to inhibit E. coli growth under either set of conditions. Thus, the active molecules identified herein may provide the basis for the development of anti-mycobacterial agents against Mtb.