Publications by authors named "Alexander Lobov"

17 Publications

  • Page 1 of 1

Synthesis of messagenin and platanic acid chalcone derivatives and their biological potential.

Nat Prod Res 2021 May 10:1-10. Epub 2021 May 10.

Organic Chemistry, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.

The chalcone derivatives of 20-oxo-lupanes have been synthesised and screened for some types of biological activity. Ozonolysis of lupanes afforded 20-oxo-derivatives with the following condensation using different aromatic aldehydes by Claisen‒Schmidt reaction to the target compounds. The configuration of 19-[3-(pyridin-3-yl)-prop-2-en-1-one]-fragment was established by X-ray analysis. Screening of cytotoxic activity against NCI-60 cancer cell line panel revealed, that messagenin derivative has the highest activity with GI value ranged from 0.304 to 0.804 μM. A colorimetric SRB assay revealed for the 2,30-bis-furfurylidene derivative and 30-bromo-20-oxo-29-nor-3,28-diacetoxy-betulin cytotoxic activity against breast carcinoma MCF-7 and ovarian carcinoma A2780 cell lines. Compounds and acted also as inhibitors of the enzyme -glucosidase (from ) with IC values of 1.76 μM and 3.3 μM thus being 97- and 52-fold more active than standard acarbose. Antiviral potency of compounds and against HCMV, HSV-1 and HPV is also discussed.
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http://dx.doi.org/10.1080/14786419.2021.1922904DOI Listing
May 2021

Discovery of Bivalent GalNAc-Conjugated Betulin as a Potent ASGPR-Directed Agent against Hepatocellular Carcinoma.

Bioconjug Chem 2021 04 10;32(4):763-781. Epub 2021 Mar 10.

Lomonosov Moscow State University, Moscow 119991, Russian Federation.

Herein, we describe the design, synthesis, and biological evaluation of novel betulin and -acetyl-d-galactosamine (GalNAc) glycoconjugates and suggest them as targeted agents against hepatocellular carcinoma. We prepared six conjugates derived via the C-3 and C-28 positions of betulin with one or two saccharide ligands. These molecules demonstrate high affinity to the asialoglycoprotein receptor (ASGPR) of hepatocytes assessed by in silico modeling and surface plasmon resonance tests. Cytotoxicity studies in vitro revealed a bivalent conjugate with moderate activity, selectivity of action, and cytostatic properties against hepatocellular carcinoma cells HepG2. An additional investigation confirmed the specific engagement with HepG2 cells by the enhanced generation of reactive oxygen species. Stability tests demonstrated its lability to acidic media and to intracellular enzymes. Therefore, the selected bivalent conjugate represents a new potential agent targeted against hepatocellular carcinoma. Further extensive studies of the cellular uptake in vitro and the real-time microdistribution in the murine liver in vivo for fluorescent dye-labeled analogue showed its selective internalization into hepatocytes due to the presence of GalNAc ligand in comparison with reference compounds. The betulin and GalNAc glycoconjugates can therefore be considered as a new strategy for developing therapeutic agents based on natural triterpenoids.
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http://dx.doi.org/10.1021/acs.bioconjchem.1c00042DOI Listing
April 2021

Thionation of quinolizidine alkaloids and their derivatives via Lawesson's reagent.

Nat Prod Res 2021 Jan 4:1-6. Epub 2021 Jan 4.

Ufa Institute of Chemistry of the Ufa Federal Research Center of Russian Academy of Sciences, Ufa, Russian Federation.

Direct thionation of quinolizidine alkaloids (-)-cytisine, methylcytisine, thermopsine and some of their carbonyl derivatives was realized. It was established that carrying out of the reaction in the boiling toluene with 0.5 eq. of Lawesson's reagent (LR) is most effective for synthesis of thio analogues of methyl-, allyl-, benzylcytisine and thermopsine. It was found, that formation of thioamides is preferable in the case with starting 3-carboxamides of (-)-cytisine or 2-oxo and 4-oxo derivatives of methylcytisine; and an excess of LR is needed for their exhaustive thionation. It was shown, that thionation of 'cytisine substituted' urea and thiourea, as well as Diels-Alder adducts of methylcitisine with phenylmaleimide on basis of this approach was not quite successful: only thionation of the 2-pyridone core has occurred. It should be noted that transformation of urea and thiourea is complicated by side reactions leading to low yields of thio products, and the result of LR interaction with mentioned above diastereomeric Diels-Alder adducts depends on their stereochemistry and thermodynamic stability under reaction conditions.
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http://dx.doi.org/10.1080/14786419.2020.1868460DOI Listing
January 2021

Allobetulone rearrangement to l8αH,19βH-ursane triterpenoids with antiviral activity.

Nat Prod Res 2020 Dec 8:1-11. Epub 2020 Dec 8.

Ufa Institute of Chemistry UFRC RAS, Ufa, Russian Federation.

Allobetulone E-ring rearrangement under treating with HClO in AcO under reflux afforded new triterpenoids: 3,28-diacetoxy-21-acetyl-2(3),20(21)-18α,19βH-ursandiene and 3,28-diacetoxy-2(3),18(19)-oleandiene . 18α,19βH-Ursanes were transformed at A- and E-rings into indolo- and bis-furfurylidene derivatives. Structure elucidation was performed using COSY, NOESY, HSQC and HMBC experiments, and X-Ray analysis for . The potential of newly obtained 18α,19βH-ursanes was evaluated against HCMV and HPV-11, the NCI-60 cancer cell panel and inhibition of α-glucosidase. All of the compounds have shown viral inhibition towards HCMV compared to standard drug Acyclovir. 3β-Acetoxy-21β-acetyl-20β,28-epoxy-18α,19βН-ursane showed moderate activity (EC 4.87 μM) towards the HCMV-resistant isolate (GDGr K17) compared to standard drug Cidofovir and was four times more potent than Ganciclovir. Compound inhibited the cell growth of the three melanoma and one colon cancer cell. 3-Oxo-21β-acetyl-20β,28-epoxy-18α,19βН-ursane and compound inhibited α-glucosidase with IC 28.0 µM and 4.0 µM being from 6 to 44 times more active than acarbose.
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http://dx.doi.org/10.1080/14786419.2020.1855159DOI Listing
December 2020

Ortho-Cyclization in Asymmetrically Substituted Arylnitroso Oxides.

J Org Chem 2020 Aug 30;85(16):10813-10822. Epub 2020 Jul 30.

Ufa Institute of Chemistry, Ufa Federal Research Center of the Russian Academy of Sciences, 71 pr. Oktyabrya, Ufa 450054, Russian Federation.

The mechanism of the photooxidation of a number of asymmetrically substituted phenyl azides in acetonitrile was studied. The key intermediates of this reaction are the corresponding nitroso oxides, the unimolecular consumption of which occurs via the cis form when the terminal oxygen atom of the NOO moiety reacts with the ortho position of the aromatic ring. As a result, it is opened to form a nitrile oxide. In the case of 3-methylphenyl azide, the reaction proceeds via the cis/syn form of nitroso oxide with a regioselectivity of 91%. The methoxy substituent at the para position changes the direction of the ortho-cyclization so that it occurs via the cis/anti form of nitroso oxide independently on the nature of a meta substituent. Nitrile oxides, which are formed as a result of these transformations of nitroso oxides, are stabilized by [3 + 2] cycloaddition with acetonitrile to give 1,2,4-oxadiazoles. The observed regioselectivity of the ortho-cyclization of nitroso oxides was explained using theoretical methods. Its cause consists in the extra-stabilization of the transition state of the reaction of the cis/anti form due to a stereoelectronic effect of the -methoxy substituent.
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http://dx.doi.org/10.1021/acs.joc.0c01314DOI Listing
August 2020

Synthesis and Evaluation of New Trivalent Ligands for Hepatocyte Targeting via the Asialoglycoprotein Receptor.

Bioconjug Chem 2020 05 9;31(5):1313-1319. Epub 2020 May 9.

Chemistry Department, Lomonosov Moscow State University, Moscow, 119991, Russian Federation.

Since the asialoglycoprotein receptor (also known as the "Ashwell-Morell receptor" or ASGPR) was discovered as the first cellular mammalian lectin, numerous drug delivery systems have been developed and several gene delivery systems associated with multivalent ligands for liver disease targeting are undergoing clinical trials. The success of these systems has facilitated the further study of new ligands with comparable or higher affinity and less synthetic complexity. Herein, we designed two novel trivalent ligands based on the esterification of tris(hydroxymethyl) aminomethane (TRIS) followed by the azide-alkyne Huisgen cycloaddition with azido -acetyl-d-galactosamine. The presented triazolyl glycoconjugates exhibited good binding to ASGPR, which was predicted using molecular docking and assessed by a surface plasmon resonance (SPR) technique. Moreover, we demonstrated the low level of cytotoxicity, as well as the optimal spatial geometry and the required amphiphilic balance, for new, easily accessible ligands. The conjugate of a new ligand with Cy5 dye exhibited selective penetration into HepG2 cells in contrast to the ASGPR-negative PC3 cell line.
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http://dx.doi.org/10.1021/acs.bioconjchem.0c00202DOI Listing
May 2020

Antiviral activity of amides and carboxamides of quinolizidine alkaloid (-)-cytisine against human influenza virus A (H1N1) and parainfluenza virus type 3.

Nat Prod Res 2019 Dec 2:1-9. Epub 2019 Dec 2.

St. Petersburg Pasteur Institute, Russian Federation, St. Petersburg, Russia.

Novel derivatives of quinolizidine alkaloid ()-cytisine were synthesised. ADME properties, cytotoxicity against HEK293 cells and activity against viruses of influenza A/California/07/09(H1N1)pdm09 virus (IAV) and human parainfluenza virus type 3 (HPIV3) were evaluated. It was shown, that 9-carboxamides of methylcytisine (with phenyl and allyl urea's fragments) are most active compounds against IAV probably due to predicted peculiarity of their interactions with the 4R7B active site of IAV neuraminidase. Indexes of selectivity (SI) calculated as ratio of CC/IC of these ureas are 47 and 59 correspondingly. It was also found, that derivatives obtained from allyl isocyanate and ()-cytisine or 9,11-dibromocytisine are able to inhibit a reproduction of HPIV3 with SI = 58 and 95. Moreover, last compound - (1 ,5)--allyl-9,11-dibromo-8-oxo-1,5,6,8-tetrahydro-2-1,5-methanopyrido[1,2-][1,5]diazocine-3(4)-carboxamide with two bromine atom in 2-pyridone core of starting ()-cytisine molecule, demonstrated high activity against HPIV3 (SI = 95) and moderate activity against IAV (SI = 16).
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http://dx.doi.org/10.1080/14786419.2019.1696791DOI Listing
December 2019

Diastereoselective Synthesis of Triterpenoid 1,2,4-Trioxolanes by Griesbaum Co-ozonolysis.

J Nat Prod 2019 09 6;82(9):2550-2558. Epub 2019 Sep 6.

A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences , Moscow 119991 , Russian Federation.

Diastereoselective synthesis of triterpenoid 1,2,4-trioxolanes by Griesbaum co-ozonolysis was shown for the first time. Ozonolysis of 2-methoxyoximes (--isomers mixture) of allobetulin or methyl oleanoate with CF-ketones resulted in asymmetrical spiro-1,2,4-trioxolanes as mixtures of diastereomers in yields up to 80-85%. The configuration of the spiro-C-2 center of individual ozonides was determined by 2D NMR spectra and X-ray crystallographic analysis. The products of ozonolysis of triterpenoid 3-methoxyoximes were mixtures of regioisomeric methoxylactams. Thus, the fundamental differences in the oxidation of homologous triterpenoid 2- or 3-methoxyoximes with ozone have been established. These results may afford a new stage in the development of the Griesbaum method as applied to natural compounds and biologically active peroxides.
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http://dx.doi.org/10.1021/acs.jnatprod.9b00393DOI Listing
September 2019

Synthesis of new 1,3-thiazol derivatives of maleopimaric acid as anticancer, antibacterial and antifungal agents.

Nat Prod Res 2021 Apr 20;35(8):1340-1348. Epub 2019 Aug 20.

Institute of Biochemistry and Genetics, Ufa Federal Research Centre of the Russian Academy of Sciences, Ufa, Russian Federation.

A series of new 1,3-thiazole derivatives of maleopimaric acid , were synthesized and evaluated for anticancer, antibacterial and antifungal activities. Evaluation of cytotoxic activity against human embryonic kidney 293 cells (HEK293), human neuroblastoma cell line (SH-SY5Y), hepatocellular carcinoma cell line (HepG2) and human T-cell lymphoblast-like line (Jurkat), showed that introduction of the aminothiazole fragment at position 6 of the diterpenoid molecule leads to decrease of cell viability. Substance 3 was found to be the most active against all tested cell lines, inhibiting cell viability with IC values in the range of 2-24 μM. The structure-activity relationship of these compounds was studied and the results show that the compounds and exhibited antifungal activity against and also possessed antibacterial profile against , , , , and .
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http://dx.doi.org/10.1080/14786419.2019.1648459DOI Listing
April 2021

Variation of spacer type and topology of phenyl moiety in 2-pyridone core of 4-oxo-3--methylcytisine; effect of synthesized compounds on rat's behavior in conditioned passive avoidance reflex (CPAR) test.

Nat Prod Res 2021 Jan 29;35(2):207-215. Epub 2019 May 29.

Laboratory of bioorganic chemistry and catalysis, Ufa Institute of Chemistry UFRC RAS, Ufa, Russian Federation.

Novel derivatives of 4-oxo-3-methylcytisine with phenyl moiety bonded to starting molecule through various spacers were obtained from the 9-amino, -halo, -formyl and 11-halo precursors by reductive alkylation of amines, generation of amide, as well as thio- and carboxamide functions, cross-coupling reactions, aldehyde condensation and reduction of unsaturated 'C-C' bonds. Ability of synthesized compounds to influence the learning and memory was preliminary assessed in conditioned passive avoidance reflex (CPAR) test in rats. It was shown, that derivatives with phenyl group at 11 carbon atom influence the learning and memory in CPAR test more effectively than other compounds. The hit-compound (3-methyl-11-(2-phenylvinyl)-3,5,6-trihydro-2H-1,5-methanopyrido[1,2-a][1,5]diazocine-4,8(1H)-dione) with the best values of 'latency' and 'time spent in the dark compartment' has been identified as a perspective scaffold for synthesis of novel derivatives of (-)-cytisine with potential neuropharmacological activity.
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http://dx.doi.org/10.1080/14786419.2019.1622106DOI Listing
January 2021

Comparative study of chemical and topological structure of macromolecules of lignins of birch (Betula verrucosa) and apple (Malus domestica) wood.

Int J Biol Macromol 2019 May 23;128:40-48. Epub 2019 Jan 23.

Institute of Chemistry of the Ufa Scientific Center of RAS, prosp. Oktyabrya, 71, Ufa 450054, Bashkortostan Republic, Russia.

Recent advances in investigations of chemical structure of lignin give rise to questions about relationship between chemical structure and topology of the macromolecules. In this paper, we made a comparison of results of the studies of chemical and topological structures of lignins. The features of topological structure of lignins of birch and apple wood were identified on the basis of the study of dilute solutions of the lignins by the sedimentation-diffusion analysis and viscometry. The number of branches of macromolecules in the birch and apple lignins was calculated by the Zimm-Kilb equation. Quantitative characteristics of chemical structure of the lignins were obtained by 2D NMR spectroscopy and nitrobenzene oxidation. The structural analysis and the calculations based on the hydrodynamic data gave estimation of the degree of branching of macromolecules, which fit well in the theory on the role of dibenzodioxocin and 4'-O-5 structures in branching of lignin macromolecules.
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http://dx.doi.org/10.1016/j.ijbiomac.2019.01.095DOI Listing
May 2019

Synthesis of A-ring quinolones, nine-membered oxolactams and spiroindoles by oxidative transformations of 2,3-indolotriterpenoids.

Org Biomol Chem 2019 01;17(3):585-597

Ufa Institute of Chemistry - Subdivision of the Ufa Federal Research Centre of Russian Academy of Sciences, Ufa 450054, Russian Federation.

This paper describes an access to new nitrogen-containing heterocyclic triterpenoids by the reaction of 2,3-indolotriterpenoids with ozone and dimethyldioxirane. The oxidation of indolo-fused 28-oxo-allobetulin or methyl platanoate with ozone led to a mixture of a quinolone as the major product and a nine-membered 2,3-seco-2-oxolactam and three different types of spiroindoles as byproducts. The formation of quinolone and 2,3-seco-2-oxolactam derivatives could be explained by the standard 1,3-dipolar cycloaddition of ozone to the C2(3)-double bond of the triterpene core similar to the products observed in the ozonolysis of indoles in the Witkop-Winterfeldt oxidation (WWO). The formation of spiroindoles was unexpected and could be explained through the 1,2-cycloaddition of ozone to the C2(3)-double bond with consecutive intramolecular rearrangements of the 2,3-epoxy-intermediate. These spiroindoles seem to be novel structures observed in the WWO reaction. The formation of only two isomeric triterpene spiroindolinones was achieved by the oxidation of 2,3-indolo-28-oxo-allobetulin with dimethyldioxirane that could be explained by the rearrangement of the 2,3-epoxy-intermediate. 19β,28-Epoxy-18α-olean-28-oxo-2-nor-2,3-4'(1H)-quinolone was the most active against HPV-11 with EC50 0.45 μM and SI50 322 in a primary assay and SI90 < 10 against HPV-16 in a secondary assay. The oxidative transformations of indolotriterpenoids have great potential for further modifications towards the preparation of new biologically active compounds.
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http://dx.doi.org/10.1039/c8ob02624fDOI Listing
January 2019

Direct formylation of 2-pyridone core of 3--methylcytisine via Duff reaction; synthesis of 9-enyl, 9-ynyl and 9-imino derivatives.

Nat Prod Res 2019 Jul 24;33(13):1897-1902. Epub 2018 May 24.

a Ufa Institute of Chemistry - Subdivision of the Ufa Federal Research Centre of Russian Academy of Sciences , Ufa , Russian Federation.

The first direct synthesis of 3--methyl-9-formylcytisine via electrophylic formylation is described. It is established, that Vilsmeier-Haack and Gatterman variants of this reaction are unsuccessful in the case with 3-substituted (-)-cytisine derivatives, but Duff procedure (with hexamethylenetetramine in trifluoroacetic acid) gives a possibility to obtain the target pseudo aromatic aldehyde with the 69% yield. Convenient precursors for [4 + 2]- or [3 + 2]-cycloaddition reactions are obtained by means of condensation of synthesized 3--methyl-9-formylcytisine with acetone, nitromethane and phosphorous ylides with yields from 70 to 87%. Alternative aprroach to alkenyl products and to 9-alkynyl-3-methylcytisine is realized using the Heck and Sonogashira cross-coupling reactions of methyl vinyl ketone, cyclohexenone or trimethylsilylacetylene with 9-bromo-3-methylcytisine (55, 70 and 60% accordingly). It is shown, that interaction of 3--methyl-9-formylcytisine with hydroxylamines leads to corresponding nitrone (93%) and oxime (70%). All individual compounds are isolated by column chromatography and completely characterized on the basis of NMR spectroscopy data.
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http://dx.doi.org/10.1080/14786419.2018.1478832DOI Listing
July 2019

Interplay of Conformational and Chemical Transformations of Ortho-Substituted Aromatic Nitroso Oxides: Experimental and Theoretical Study.

J Org Chem 2017 08 20;82(15):7750-7763. Epub 2017 Jul 20.

Ufa Institute of Chemistry of the Russian Academy of Sciences , 71 pr. Oktyabrya, Ufa 450054, Russian Federation.

The mechanism of the photooxidation of aromatic azides containing a substituent at one of the ortho positions (2,4-dimethoxyphenyl azide (1a) and 2-methyl-4-[(2E)-1-methylbut-2-en-1-yl]phenyl azide (1b)) was studied in acetonitrile. The electronic spectra and the kinetic regularities of the consumption of corresponding nitroso oxides, which are the reaction intermediates, were investigated by flash photolysis. Owing to the one-and-a-half order of the C-N and N-O bonds and asymmetric molecule structure these nitroso oxides exist as four conformers (cis/syn, cis/anti, trans/syn, and trans/anti). The conformers differ in the spectral properties and in the reactivity in various irreversible transformations. The only product, (2Z,4E)-4-methoxy-6-oxohepta-2,4-dienenitrile oxide (7a), was observed during photooxidation of 1a, whereas transformations of the nitroso oxide isomers derived from 1b led to a set of stable products: the cis/anti isomer was transformed into (3,4,7-trimethyl-3a,4-dihydro-2,1-benzisoxazol-5(3H)-ylidene)ethanal (10), the trans isomers recombined forming the corresponding nitro and nitroso compounds, and the most reactive cis/syn isomer was transformed into ortho-nitrosobenzyl alcohol 11. The last was oxidized slowly to the corresponding benzaldehyde 12. Interaction of 11 and 12 led to the formation of (Z)-1,2-bis(2-formyl-4-((2E)-1-methylbut-2-en-1-yl)phenyl)diazene-1-oxide (13). The DFT simulation and kinetic modeling of the nitroso oxide transformations as well as the product analysis allowed revealing the fine details of the mechanism of decay for these species.
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http://dx.doi.org/10.1021/acs.joc.7b00537DOI Listing
August 2017

Nature of Lewis Base Catalysis of 1,3-Dipolar Cycloaddition of Methyl Diazoacetate to Methyl Acrylate; NMR Kinetic Spectroscopy and DFT Study.

J Phys Chem B 2017 07 27;121(27):6601-6609. Epub 2017 Jun 27.

Ufa Institute of Chemistry of the Russian Academy of Sciences , 71 Prospect Oktyabrya, 450054 Ufa, Russia.

The effect of Lewis base (LB) in the domino reaction between methyl diazoacetate and methyl acrylate has been studied. This domino process is initialized by a [3+2]-cycloaddition reaction to generate 3H-pyrazoline followed by a subsequent 1,3-H shift reaction forming 1H-pyrazoline as the more stable isomer. The rate of the first step is not sensitive to the presence of LBs (THF, Py, DMAP, DBU, and triphenylphosphine) as it was evidenced by kinetic nuclear magnetic resonance spectroscopy and quantum chemical modeling. LBs manifest remarkable catalytic effect on the second step of the reaction only acting as proton acceptor. DFT calculations reveal fine correlation between enthalpy of proton transfer from trans-3H-pyrazoline to LB and basic strength of the latter described in terms of BF-affinity scale. Under conditions of LB catalysis the reaction rate of the first step (methyl diazoacetate and methyl acrylate interaction) limits the rate of 3H → 1H pyrazoline isomerization and, therefore, restricts catalytic efficiency of LB. An alternative mechanism for catalysis of the 1,3-dipolar cycloaddition through formation of triazene-like intermediate during reaction of diazo acetate with LB and following Michael addition of intermediate to alkene was carefully analyzed. This reaction scheme was not confirmed in our experiments.
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http://dx.doi.org/10.1021/acs.jpcb.7b02064DOI Listing
July 2017

Stereospecific Oxidation of Diacetoxyheterobetulin with Ozone and Dimethyldioxirane.

Nat Prod Commun 2016 Apr;11(4):449-52

Stereospecific oxidation of diacetoxyheterobetulin with ozone and dimethyldioxirane led to 3β,28-diacetoxy-18α,19βH-urs-20α,21α-epoxide with yields of 79% and 87%, respectively. Oxidation with ozone was not selective and gave two minor products containing 2lα-hydroxy-20(30)-ene and 21a-hydroxy-20β,28-epoxy-fragments in ring E. The structures of 3β,28-diacetoxy-18α,19βH-urs-20α,21α-epoxide and 3β-diacetoxy-21α-hydroxy-20β,28-epoxy-18α,19βH-ursane were confirmed by X-ray analysis for the first time.
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April 2016

Aza-Michael reaction of 12-N-carboxamide of (-)-cytisine under high pressure conditions.

Nat Prod Res 2015 21;29(2):141-8. Epub 2014 Oct 21.

a Institute of Organic Chemistry, Ufa Scientific Center of the Russian Academy of Sciences , 71, pr. Oktyabrya, 450054 Ufa , Russian Federation.

The first example of aza-Michael reaction of 12-N-carboxamide of quinolizidine alkaloid (-)-cytisine with α,β-unsaturated ketones, dimethyl acetylenedicarboxylate and β-nitrostyrene under high pressure condition has been described. It has been shown that the [4+2]-cycloaddition takes place in the case with N-phenylmaleimide.
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http://dx.doi.org/10.1080/14786419.2014.968150DOI Listing
April 2015