(±)-cis-(6-Ethyl-tetrahydropyran-2-yl)-formic acid: a novel substance with antinociceptive properties

The Role Ionic Liquid [BMIM][PF6] in One-Pot Synthesis of Tetrahydropyran Rings through Tandem Barbier-Prins Reaction

Tetrahydropyran (THP) rings are common in several natural products, therefore, various strategies are being developed to synthesize these rings. The present work described the study of a one-pot synthesis of 2,4,6-trisubstituted tetrahydropyran compounds promoted by the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] through a Barbier-Prins reaction between allyl bromide and aldehydes. The use of [BMIM][PF6] gave Prins products from several aldehydes in good yields and reaction times. We also found that the anion, PF6-, accelerates the Barbier reaction when used alone, and the excess SnBr2 from the reaction conditions of the Barbier reaction leads to the formation of the THP rings, thus acting as a catalyst for Prins cyclization. Additionally, we demonstrate that ionic liquid can be recovered and reused five times in the preparation of 4-bromo-tetrahydro-2,6-diphenyl-2H-pyran without significant yield loss.

Antihyperalgesic effect of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol: participation of the NO/cGMP/KATP pathway and κ-opioid receptor

The present study used behavioral analyses to investigate the involvement of the NO/cGMP/KATP pathway, serotoninergic, and opioid systems in the antinociceptive action of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol (CTHP) in mice. Oral administration of CTHP (1, 5, 10, and 30 mg/kg) exerted effects at higher doses in chemical models of nociception (the acetic acid writhing and formalin tests) as well as a thermal model (the tail-flick test). It was also found that pretreatment with L-N-nitroarginine methyl ester (nonselective nitric oxide synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (selective inhibitor of nitric oxide-sensitive guanosyl cyclase), glibenclamide (selective ATP-sensitive K channel blocker), naloxone (nonselective opioid receptor blocker), and nor-binaltorphimine (selective κ-opioid receptor blocker), but not methylnaltrexone (peripheral μ-opioid receptor blocker) or naltrindole (selective δ-opioid receptor blocker), reversed the antinociceptive effect of CTHP. In addition, CTHP induced the development of tolerance in the tail-flick test: the tolerance appeared later compared with morphine, and was only observed with a higher dose. Taken together, the present study showed that the systemic administration of CTHP reduced pain induced by chemical and thermal stimuli. We also suggest that the possible mechanisms include the involvement of the NO/cGMP/KATP pathway and the κ-opioid receptor.

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/anti-inflammatory 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 (SI_rb > 180.19), compared with the highly-toxic reference drug (SI_rb = 33.05), indicating that the bromine hybrid is a promising compound for further biological studies.

Synthesis and Anticancer Activities of Novel Guanylhydrazone and Aminoguanidine Tetrahydropyran Derivatives

In this paper we present the convenient syntheses of six new guanylhydrazone and aminoguanidine tetrahydropyran derivatives 2-7. The guanylhydrazone 2, 3 and 4 were prepared in 100% yield, starting from corresponding aromatic ketones 8a-c and aminoguanidine hydrochloride accessed by microwave irradiation. The aminoguanidine 5, 6 and 7 were prepared by reduction of guanylhydrazone 2-4 with sodium cyanoborohydride (94% yield of 5, and 100% yield of 6 and 7). The aromatic ketones 8a-c were prepared from the Barbier reaction followed by the Prins cyclization reaction (two steps, 63%-65% and 95%-98%). Cytotoxicity studies have demonstrated the effects of compounds 2-7 in various cancer and normal cell lines. That way, we showed that these compounds decreased cell viabilities in a micromolar range, and from all the compounds tested we can state that, at least, compound 3 can be considered a promising molecule for target-directed drug design.

Structural determination Vitex cymosa Bertero active principle: Diastereoselective synthesis of (+/-)-trans-4-hydroxy-6-propyl-1-oxocyclohexan-2-one and its antinociceptive activity

The diastereoselective synthesis of (+/-)-trans-4-hydroxy-6-propyl-1-oxocyclohexan-2-one, as a mixture trans:cis (3:1), was accomplished using a protocol that combine the Prins cyclization and RuO(4) oxidation. The synthesis this lactone allowed the elucidation of the correct structure of the substance isolated from the barks of Vitex cymosa. The delta-lactones mixture showed significant antinociceptive properties in preliminary tests using the tail flick model assay.

Antinociceptive action of (±)-cis-(6-ethyl-tetrahydropyran-2-yl)-formic acid in mice

The objective of this study was to investigate spinal and supraspinal antinociceptive effects of a new synthetic compound, (+/-)-cis-(6-ethyl-tetrahydropyran-2-yl)-formic acid (tetrahydropyran derivative). Its activity was compared with those from morphine. In peripheral models of inflammation and hyperalgesia, tetrahydropyran derivative significantly reduced nociceptive effect induced by acetic acid or formalin in mice. Tetrahydropyran derivative developed antinociceptive effect on the tail-flick and hot-plate tests with a long-acting curve maintaining the effect for 4 h longer than morphine. The opioid receptor antagonist naloxone totally reverted tetrahydropyran derivative effects on both models. Morphine as well as tetrahydropyran derivative induced tolerance and sedation in mice. However, tetrahydropyran derivative-induced tolerance had its onset retarded and the sedative activity was lower when compared to that induced by morphine. These results indicate that this new substance develops an antinociceptive activity and may be used in the future as a substitute for traditional opioids.

High selective leishmanicidal activity of 3-hydroxy-2-methylene-3-(4-bromophenyl)propanenitrile and analogous compounds

Sixteen not new aromatic compounds were prepared by one-pot reaction i.e. through Baylis-Hillman reaction and were the first time evaluated against promastigote Leishmania amazonensis and infected mammalian cells. Most of the compounds were selectively more active against amastigotes than the reference drug sodium stibogluconate (Pentostam, IC(50)=44.7 microM). We found that 3-hydroxy-2-methylene-3-(4-bromophenyl) propanenitrile (13) was the most active (IC(50)=12.5 microM) and safer compound (0.0 (0.9); % macrophage LDH release), being the lead compound.

5-Exocyclic Products, 2,3,5-Trisubstituted Tetrahydrofurans via Prins-Type Cyclization

[reaction: see text] 5-Exocyclic products, 2,3,5-trisubstituted tetrahydrofurans, were synthesized from homopropargylic alcohols with terminally substituted alkynes and various aldehydes via Prins-type cyclization. It is of interest that the exocyclic vinyl cation generated as a result of Prins-type cyclization could be trapped as a vinyl triflate when CH2Cl2 was used as a solvent, whereas in ethereal solution the vinyl cation underwent hydrolysis to give the corresponding ketone product.

Baylis-Hillman adducts with molluscicidal activity against Biomphalaria glabrata

The molluscicidal activities of ten Baylis-Hillman adducts against Biomphalaria glabrata (Say) snails, the intermediate host of schistosomiasis, have been determined. Nine of these compounds showed significant molluscicidal activity against B. glabrata, falling below the threshold of 100 microg ml(-1) set for potential molluscicidal activity by the World Health Organisation. Among these compounds, 3-hydroxy-2-methylene-3-(4-nitrophenyl)propanenitrile had the highest activity, with LC(50) = 6.64 microg ml(-1).