Synthesis of ß-Amino Acid Derivatives via Enantioselective Lewis Base Catalyzed N-Allylation of Halogenated Amides with Morita-Baylis-Hillman Carbonates.

Trifluoro- and trichloroacetamides serving as pronucleophiles undergo enantioselective Lewis base catalyzed N-allylation with Morita-Baylis-Hillman carbonates to produce enantioenriched ß-amino acid derivatives. The reactions proceed as a kinetic resolution to give the allylation products and the remaining carbonates in good yields and high enantioselectivity. The obtained products are amenable to diastereoselective derivatization to produce a library of spiro-isoxazoline lactams.

Xanthopsin-Like Systems via Site-Specific Click-Functionalization of a Retinoic Acid Binding Protein.

The use of light-responsive proteins to control both living or synthetic cells, is at the core of the expanding fields of optogenetics and synthetic biology. It is thus apparent that a richer reaction toolbox for the preparation of such systems is of fundamental importance. Here, we provide a proof-of-principle demonstration that Morita-Baylis-Hillman adducts can be employed to perform a facile site-specific, irreversible and diastereoselective click-functionalization of a lysine residue buried into a lipophilic binding pocket and yielding an unnatural chromophore with an extended π-system. In doing so we effectively open the path to the in vitro preparation of a library of synthetic proteins structurally reminiscent of xanthopsin eubacterial photoreceptors. We argue that such a library, made of variable unnatural chromophores inserted in an easy-to-mutate and crystallize retinoic acid transporter, significantly expand the scope of the recently introduced rhodopsin mimics as both optogenetic and "lab-on-a-molecule" tools.

Leishmanicidal activity of Morita-Baylis-Hillman adducts.

Leishmaniasis is a neglected disease that affects millions of people, mostly in developing countries. Although this disease has a high impact on public health, there are few drug options to treat the different leishmaniasis forms. Additionally, these current therapies have various adverse effects, including gastrointestinal disturbances, headache, pancreatitis, and hepatotoxicity. Thus, it is essential to develop new drug prototypes to treat leishmaniasis. Accordingly, the present study aimed to evaluate the leishmanicidal activity of Morita-Baylis-Hillman adducts and their O-acetylates, carboxylic acid derivatives, and acid and ester derivatives of 2-methyl-phenylpropanoids against Leishmania chagasi. Initially, we evaluated the cytotoxicity of 16 derivatives (1-16G) against J774A.1 macrophages. Eight derivatives (2G, 4G, 5G, 7G, 9G, 10G, 13G, and 15G) showed no cytotoxicity at up to the maximum concentration tested (100 µM). When evaluated for antileishmanial effect against promastigote forms, 1G, 6G, 8G, 10G, 11G, 13G, 14G, 15G, and 16G displayed significant toxicity compared to the control (0.1% DMSO). Additionally, the compounds 1G, 5G, 7G, 9G, 11G, 13G, 14G, and 16G reduced macrophage infection by amastigotes. Thus, we conclude that these derivatives have antileishmanial effects, particularly 1G, which showed activity against promastigotes and amastigotes, and low toxicity against macrophages.

Facile and innovative catalytic protocol for intramolecular Friedel-Crafts cyclization of Morita-Baylis-Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF3·OEt2 catalysis.

The chiral (salen)Cr(III)/BF3·OEt2 catalytic combination was found to be an effective catalyst for intramolecular Friedel-Crafts cyclization of electron-deficient Morita-Baylis-Hillman adducts. In presence of mild reaction conditions the chiral (salen)Cr(III)/BF3·OEt2 complex affords 2-substituted-1H-indenes from unique substrates of Morita-Baylis-Hillman adducts via an easy operating practical procedure.

Synthesis, anti-proliferative activity, theoretical and 1H NMR experimental studies of Morita-Baylis-Hillman adducts from isatin derivatives.

Quaternary or spirocyclic 3-substituted-3-hydroxy-2-oxindole is considered a privileged scaffold. In other words, it is a molecular core present on several compounds with a wide spectrum of biological activities. Among its precursors, activated ketones (isatin nucleus) can be used as interesting starting points to Morita-Baylis-Hillman adducts derivatives, a class of compounds with good cytotoxic potential. In this paper, we present the synthesis, anti-proliferative activity against lung cancer cell line and a theoretical conformational study of 21 of Morita-Baylis-Hillman adducts from isatin derivatives, by DFT quantum chemical calculations, followed by a SAR and QSAR analysis. Besides, an efficient synthetic protocol and good biological activity profile were highlighted interesting observations about 1H NMR experimental spectra, molecular modeling results and crystallographic data available.

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita-Baylis-Hillman adducts.

The direct transformation of Morita-Baylis-Hillman (MBH) adducts into molecules of interest is a crucial process wherein allylic hydroxy-protected or halogenated MBH adducts are commonly preferred. Herein, we report an azidophosphonium salt (AzPS)-catalysed straight forward protocol for synthesising structurally demanding (E)/(Z)-cinnamyl-1H-1,2,3-triazoles and halomethylcoumarins from MBH adducts. The novel methodology, efficient catalyst, and direct utilization of MBH adducts under mild reaction conditions qualify the reported procedures as powerful synthetic tools.

Anti-melanogenesis potential of a new series of Morita-Baylis-Hillman adducts in B16F10 melanoma cell line.

Melanin is a natural polymer pigment which provides skin photoprotection against ultraviolet radiation. An excessive synthesis of melanin leads to hyperpigmentation disorders. Tyrosinase catalyzes the rate limiting steps on melanogenesis. Therefore, tyrosinase inhibitors have potential applications in medicine and cosmetic fields. We carried out herein the screening of a family of cyclic Morita-Baylis-Hillman adducts (MBH) to find out their effects on tyrosinase activity and on melanogenesis in murine melanoma B16F10 cell line. Kinetic analysis of tyrosinase inhibition showed that compounds 1a (2-hydroxymethyl) cyclohex-2-enone) and 3f (diethyl (1-(6-oxocyclohex-1-en-1-yl) ethyl-phosphonate) were competitive inhibitors, whereas the compound 2b (6-oxocyclohex-1-en-1-yl) ethyl acetate) was a non-competitive one. Additionally we have found that (1a, 2b and 3f) compounds had a strong melanogenesis inhibition effect in isobutylmethylxanthine (IBMX)-treated murine melanoma B16F10 cells when tested at low and non cytotoxic dose (10-50 µM), by attenuating the melanin production, intracellular tyrosinase activity and tyrosinase expression. Thus, we suggest that these compounds could be used as effective skin-whitening agents.

Palladium-Catalyzed Asymmetric Allylic Alkylations of Colby Pro-Enolates with MBH Carbonates: Enantioselective Access to Quaternary C-F Oxindoles.

Owing to the innovative applications of fluorinated compounds in many areas of technology and medicine, methods for the preparation of C-F quaternary fluorine containing compounds are in extremely high demand. Here, we report the discovery of a general procedure for an SN 2 reaction catalyzed by Pd/Ding-SKP-type ligands, and that occurs between Colby pro-enolates with MBH carbonates to afford the corresponding products featuring two consecutive stereogenic carbons, including a C-F quaternary stereogenic center. The reactions readily occur at ambient temperatures with high chemical yields and in excellent chemo-, diastereo- and enantioselective manners. This practically attractive stereochemical outcome, coupled with the operational simplicity and structural generality, bodes well for the synthetic application of this process in the preparation of a novel class of biologically relevant fluorine-containing compounds.

Potential antioxidant activity of Morita-Baylis-Hillman adducts.

The wide variety of potent biological activities of Morita-Baylis-Hillman adducts (MBH) encouraged us to synthesize new series of products belonging to this class of compounds, possessing different functionalities and exhibiting potential antioxidant activity. As part of our on-going program on targeting molecules with antioxidant activity, we describe herein different DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activities of MBH alcohols and their derivatives including acetates, phosphonates and hydrazonophosphonates. The obtained results showed that the strongest DPPH radical scavenging activity was observed in the case of hydrazonophosphonates in comparison to the other MBH derivatives.

Synthesis of 16 New Hybrids from Tetrahydropyrans Derivatives and Morita-Baylis-Hillman Adducts: In Vitro Screening against Leishmania donovani.

Leishmaniases are a group of neglected tropical diseases (NTDs) caused by protozoan parasites from >20 Leishmania species. Visceral leishmaniasis (VL), also known as kala-aza, is the most severe form of leishmaniasis, usually fatal in the absence of treatment in 95% of cases. The Morita-Baylis-Hillman adducts (MBHAs) are being explored as drug candidates against several diseases, one of them being leishmaniasis. We present here the design, synthesis and in vitro screening against Leishmania donovani of sixteen new molecular hybrids from analgesic/antiinflammatory tetrahydropyrans derivatives and Morita-Baylis-Hillman adducts. First, acrylates were synthesized from analgesic/anti-inflammatory tetrahydropyrans using acrylic acid under TsOH as a catalyst (70-75% yields). After the 16 new MBHAs were prepared in moderate to good yields (60-95%) promoted by microwave irradiation or low temperature (0 °C) in protic and aprotic medium. The hybrids were evaluated in vitro on the promastigote stage of Leishmania donovani by determining their inhibitory concentrations 50% (IC50), 50% hemolysis concentration (HC50), selectivity index (HC50/IC50,), and comparing to Amphotericin B, chosen as the anti-leishmanial reference drug. The hybrid which presents the bromine atom in its chemical structure presents high leishmanicide activity and the high selectivity index in red blood cells (SIrb > 180.19), compared with the highly-toxic reference drug (SIrb = 33.05), indicating that the bromine hybrid is a promising compound for further biological studies.

Synthesis and activity of novel homodimers of Morita-Baylis-Hillman adducts against Leishmania donovani: A twin drug approach.

It is reported here the synthesis of novel Homodimers 12-19 of Morita-Baylis-Hillman adducts (MBHA) from one-pot Morita-Baylis-Hillman Reaction (MBHR) between aromatic aldehydes as eletrophiles and ethylene glycol diacrylate as Michael acceptor (35-94% yields) using cheap and green conditions. The bioactivities were evaluated against promastigote form of Leishmania donovani. All homodimers showed to be more potent than corresponding monomers. It is worth highlighting that the halogenated homodimers 17 and 18 (0.50µM) is almost 400 times more active than the corresponding monomer 10 and 1.24 times more potent than the second-line drug amphotericin B (0.62µM). Moreover, the selectivity index to 18 is very high (SIrb>400) far better than amphotericin B (SIrb=18.73). This is the first report of twin drugs strategy applied on Morita-Baylis-Hillman adducts.

Synthesis and In Vitro Anti Leishmania amazonensis Biological Screening of Morita-Baylis-Hillman Adducts Prepared from Eugenol, Thymol and Carvacrol.

Leishmaniasis represents a series of severe neglected tropical diseases caused by protozoa of the genus Leishmania and is widely distributed around the world. Here, we present the syntheses of Morita-Baylis-Hillman adducts (MBHAs) prepared from eugenol, thymol and carvacrol, and their bioevaluation against promastigotes of Leishmania amazonensis. The new MBHAs are prepared in two steps from essential oils in moderate to good yields and present IC50 values in the range of 22.30-4.71 µM. Moreover, the selectivity index to the most potent compound is very high (SIrb > 84.92), far better than that of Glucantime® (SIrb 1.39) and amphotericin B (SIrb = 22.34). Conformational analysis were carried out at the M062X//6-31+G(d,p) level of theory to corroborate a hypothesis about the nitroaromatic bioreduction mechanism.

Novel organocatalytic activation of unmodified Morita-Baylis-Hillman alcohols for the synthesis of bicyclic α-alkylidene-ketones.

The organocatalytic activation of Morita-Baylis-Hillman alcohols via H-bonding-iminium-ion formation is demonstrated for the first time. This activation strategy enables the Morita-Baylis-Hillman alcohols to undergo a formal SN2' reaction. In combination with the well-established enamine reactivity, this creates a new reactivity pattern. The application of this new activation mode for the synthesis of bicyclic α-alkylidene-ketones is demonstrated. The developed reaction sequence proceeds efficiently affording nature-inspired target products with four contiguous stereogenic centers in a highly stereoselective manner.

Divergent pathways and competitive mechanisms of metathesis reactions between 3-arylprop-2-ynyl esters and aldehydes: an experimental and theoretical study.

Mechanistic studies of the reaction between 3-arylprop-2-ynyl esters and aldehydes catalyzed by BF3 ⋅Et2 O were performed by isotopic labeling experiments and quantum chemical calculations. The reactions are shown to proceed by either a classical alkyne-carbonyl metathesis route or an unprecedented addition-rearrangement cascade. Depending on the structure of the starting materials and the reaction conditions, the products of these reactions can be Morita-Baylis-Hillman (MBH) adducts that are unavailable by traditional MBH reactions or E- and Z-α,ß-unsaturated ketones. (18) O-Labeling studies suggested the existence of two different reaction pathways to the products. These pathways were further examined by quantum chemical calculations that employed the DFT(wB97XD)/6-311+G(2d,p) method, together with the conductor-like screening model for realistic solvation (COSMO-RS). By using the wB97XD functional, the accuracy of the computed data is estimated to be 1-2 kcal mol(-1) , shown by the careful benchmarking of various DFT functionals against coupled cluster calculations at the CCSD(T)/aug-cc-pVTZ level of theory. Indeed, most of the experimental data were reproduced and explained by theory and it was convincingly shown that the branching point between the two distinct mechanisms is the formation of the first intermediate on the reaction pathway: either the four-membered oxete or the six-membered zwitterion. The deep mechanistic understanding of these reactions opens new synthetic avenues to chemically and biologically important α,ß-unsaturated ketones.

Crystal structure of methyl 2-(2H-1,3-benzodioxol-5-yl)-7,9-di-bromo-8-oxo-1-oxa-spiro-[4.5]deca-2,6,9-triene-3-car-boxyl-ate.

The title compound, C18H12Br2O6, was synthesized from Morita-Baylis-Hillman adducts. It incorporates the bromin-ated spiro-hexa-dienone moiety typically exhibited by compounds of this class that exhibit biological activity. Both the brominated cyclo-hexa-dienone and the central five-membered rings are nearly planar (r.m.s. deviations of 0.044 and 0.016 Å, respectively), being almost perpendicularly oriented [inter-planar angle = 89.47 (5)°]. With respect to the central five-membered ring, the brominated cyclo-hexa-dienone ring, the benzodioxol ring and the carboxyl-ate fragment make C-O-C-C, O-C-C-C and C-C-C-O dihedral angles of -122.11 (8), -27.20 (11) and -8.40 (12)°, respectively. An intra-molecular C-H⋯O hydrogen bond occurs. In the crystal, mol-ecules are linked by non-classical C-H⋯O and C-H⋯Br hydrogen bonds resulting in a molecular packing in which the brominated rings are in a head-to-head orientation, forming well marked planes parallel to the b axis.