Fluorescence study on the nyctinasty of Phyllanthus urinaria L. using novel fluorescence-labeled probe compounds

We report the synthesis of fluorescence-labeled probes based on phyllanthurinolactone 1, which is a leaf-closing substance of Phyllanthus urinaria L. The fluorescence study using biologically active probe 2 and inactive probes (epi-2 and 31) revealed that the target cell for 1 is a motor cell and suggested that some receptors, which recognize the aglycon of 1 exist on the plasma membrane of the motor cell, as with leaf-opening substances. Moreover, binding of probe 2 was specific to the plant motor cell contained in the plants belonging to the genus Phyllanthus. These results showed that the binding of probe 2 with a motor cell is specific to the plant genus and suggested that the genus-specific receptor for the leaf-closing substance would be involved in nyctinasty.     

Enantio-differential approach using fluorescence-labeled phyllanthurinolactone, a leaf-closing factor of Phyllanthus urinaria L.

We report here the synthesis of enantio-pair-type fluorescence-labeled probes based on phyllanthurinolactone (1), which is a leaf-closing substance of Phyllanthus urinaria L. Moreover, the application of an enantio-differential approach to distinguish between specific and nonspecific binding of ligands and receptors was performed. Fluorescence studies using a natural-type probe 6 and a nonnatural-type probe 7 revealed that the target cell for 1 is a motor cell. Furthermore, our results lead to the suggestion that some receptors, which recognize the stereochemistry of the aglycon of 1, exist on the plasma membrane of the motor cell, as do leaf-opening substances.     

Direct observation of a target cell of the leaf-closing factor by using novel fluorescence-labeled phyllanthurinolactone

We report the synthesis of the fluorescence-labeled probe 2 based on phyllanthurinolactone 1, which is a leaf-closing substance of Phyllanthus urinaria L. Bioorganic studies using probe 2 showed leaf-closing activity at 1 × 10⁻⁵ M, which was one-hundredth of that of the natural product 1. The fluorescence study using 2 revealed that the target cell for 1 is a motor cell and suggested that some receptors for 1 exist on the plasma membrane of the motor cell as with leaf-opening substances.     

Synthesis of UDP-GalNAc analogues as probes for the study of polypeptide-α-GalNAc-transferases. Part 2

The synthesis of four UDP-GalNAc analogues (1-4) is described. The 3-, 4- and 6-deoxygenated analogues 1-3 were obtained by way of a divergent strategy starting from a 3,6-di-O-pivaloyl GlcNAc derivative as a common precursor. Analogue 4 bearing a N-trifluoroacetamido group was prepared from the trifluoromethylated oxazoline 24 as key intermediate. These compounds were designed to probe the substrate specificity of polypeptide-α-GalNAc transferases.     

Self-assembly of a new series of quadruply hydrogen bonded heterotrimers driven by the donor-acceptor interaction

This paper describes the self-assembly of a new series of heterotrimers in chloroform-d by utilizing the cooperative interaction of hydrogen bonding and donor-acceptor interaction. Compounds 1 and 11, in which an 2-ureido-4[1H]-pyrimidinone unit is connected to 34-crown-10 or 36-crown-10, were used as donor monomer, and 2 and 19, in which an 2-ureido-4[1H]-pyrimidinone unit is connected to NDI, were used as acceptor monomer, while linear compound 4, which contains two diamido-1,8-naphthyridines, was used as template. A large tri-p-(t-butyl)phenylmethoxyl group was introduced to 19 in order to compare its assembling behavior with that of 2. Mixing 4 with dimer 1·2 caused 1·2 to fully decompose and to afford 55% of ‘in-in’-oriented heterotrimer 1·4·2. Adding 4 to the solution of 2·11 or 11·19 in chloroform-d also led to full dissociation of the dimers. However, in these systems the ‘in-in’-arranged heterotrimer 2·4·11 or 11·4·19 could be produced exclusively.     

Palladium-catalyzed asymmetric synthesis of allylic alcohols from unsymmetrical and symmetrical racemic allylic carbonates featuring C-O-bond formation and dynamic kinetic resolution

Described is the asymmetric synthesis of the allylic alcohols 11 (85% ee), 15 (99% ee), 17 (93% ee), 19 (61% ee), and 21 (69% ee) through a Pd-catalyzed reaction of the unsymmetrical carbonates rac-10, rac-12, rac-14, rac-16, rac-18, and rac-20, respectively, with KHCO₃ and H₂O in the presence of bisphosphane 6. Similarly the allylic alcohols 23 (99% ee) and 25 (97% ee) have been obtained from the symmetrical carbonates rac-22 and rac-24, respectively. Reaction of the meso-biscarbonate 26 with H₂O and Pd(0)/6 afforded alcohol 27 (96% ee), which was converted to the PG building block 32. The unsaturated bisphosphane 33 showed in the synthesis of alcohols 36, 37, and 39 a similar high selectivity as 6. The formation of alcohols 11, 15, and 17 involves an efficient dynamic kinetic resolution.     

Microbial transformations of buagarofuran,an anti-anxietic agent

19 structurally diverse metabolites (2–20) were isolated from the transformation of buagarofuran (1), an anxiety agent, by three filamentous fungal strains, Cunninghamella echinulata AS 3.3402, Cunninghamella elegans AS 3.3400, and Absidia coerulea AS 3.3538. Their structures and identified on the basis of extensive spectroscopic data (HRMS, NMR, IR, and CD) and chemical methods. All of the metabolites were oxidized products of 1, and metabolite 20 was also one of mammalian metabolites. Metabolites 8, 10–12, and 20 significantly inhibited [³H]-NE re-uptake, and 8 and 9 strongly inhibited [³H]-5-HT re-uptake in the rat brain synaptosomes at 10 μM in vitro. The structural diversity of the microbial transformed metabolites of buagarofuran in the present report would give a favorable opportunity to probe its mammalian metabolism and better shed light on its pharmacokinetics and pharmacodynamics in vivo.     

Synthesis of pyrrolo[3,2-b]benzofurans and pyrrolo[3,2-b]naphthofurans via addition of a silyloxypyrrole to activated quinones

The uncatalyzed reaction of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 with 1,4-quinones bearing an electron withdrawing group at C-2 has been studied. Use of 1,4-quinones 4, 5 bearing an ester group at C-2 provided an efficient synthesis of the respective pyrrolidinobenzofuran adduct 9 or pyrrolidinonaphthofuran adduct 10 whereas use of 1,4-quinones 6, 7 and 8 bearing an acetyl group at C-2 afforded silyloxypyrroles 11, 12 and 13 resulting from direct electrophilic substitution of the silyloxypyrrole by the electrophilic quinone. Addition of Eu(fod)₃ to the reaction of 2-acetyl-1,4-naphthoquinone 7 and 3-acetyl-5-methoxy-1,4-naphthoquinone 8 with N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole 3 provided a method for obtaining the pyrrolidinonaphthofuran adducts 14 and 15 together with silyloxypyrroles 12 and 13. Oxidative rearrangement of pyrrolidinonaphthofuran adduct 15 to pyrrolidino pyranonaphthoquinone 16 using ceric ammonium nitrate in acetonitrile provided a novel approach for the synthesis of an aza-analogue of the pyranonaphthoquinone antibiotic kalafungin.     

Synthesis of the 4-methyl-1,2-oxazetidine-4-carboxylic acid moiety of the originally proposed halipeptin A and B structures

O-Alkylation of N-hydroxycarbamate 6 with iodo ester 5 affords 15, which was elaborated to mesylate 4. Intramolecular N-alkylation affords methyl N-Boc-4-methyl-1,2-oxazetidine-4-carboxylate (3). The geminal coupling constant of the methylene protons is 8.5 Hz, which is much smaller than the 12.0 Hz reported for halipeptins A and B. This confirms that the halipeptins do not contain an oxazetidinecarboxylic acid as originally proposed in structure 1, but a thiazoline as in the revised structure 2. The unusual O-alkylation of 5 probably proceeds by an electron transfer mechanism.     

Highly efficient, multigram and enantiopure synthesis of (S)-2-(2,4′-bithiazol-2-yl)pyrrolidine

(S)-2-(4-Bromo-2,4′-bithiazole)-1-(tert-butoxycarbonyl)pyrrolidine ((S)-1) was obtained as a single enantiomer and in high yield by means of a two-step modified Hantzsch thiazole synthesis reaction when bromoketone 3 and thioamide (S)-4 were used. Further conversion of (S)-1 into trimethyltin derivative (S)-2 broadens the scope for further cross-coupling reactions.     

Imino Diels-Alder reaction of boronates. Preparation and characterization of new 3,4-dihydroquinoline and 1,2,3,6-tetrahydropyridine derivatives

The preparation of 3,4-dihydroquinolines (2a-d and 3a,b,d), as well as 1,2,3,6-tetrahydropyridines (4a-e) by imino Diels-Alder reaction of boronates (1a-e) with 2,3-dimethylbutadiene is reported. Boronates (1a-d) containing substituents meta and para relative to the imino fragment lead to diastereomeric mixtures of 4-methyl-4-ethenyl-3,4-dihydroquinolines (2, 3) and tetrahydropyridines (4). In contrast, the presence of an electron withdrawing substituent at the para position (1e), favors the iminodienophile behavior giving 4,5-dimethyl-1,2,3,6-tetrahydropyridine (4e) as the main product. The results show that boronates derived from Schiff bases are electron deficient species which can act either as dienophiles or dienes in the reaction with 2,3-dimethylbutadiene to give 3,4-dihydroquinolines and 1,2,3,6-tetrahydropyridines. All products were characterized by NMR and X-ray diffraction analysis of 2b, 2d, 3d and 4c allowed to assign the relative configuration of the newly formed stereogenic centers.     

A facile electrochemical method for the synthesis of phenazine derivatives via an ECECC pathway

Electrochemical oxidation of 2,3-dimethylhydroquinone 1 has been studied in the presence of o-phenylenediamines 3a-c as nucleophiles in aqueous solution, using cyclic voltammetry and controlled potential coulometry. The results indicate that the quinone 2 derived from 2,3-dimethylhydroquinone participates in Michael addition and imine condensation reactions with o-phenylenediamine via an ECECC mechanism, and is converted to the corresponding phenazine derivatives 7a-c and 7′b. The electrochemical synthesis of compounds 7a-c and 7′b has been performed successfully at a carbon rod electrode in an undivided cell with good yields and high purities.     

Novel taxoids from the Chinese yew Taxus yunnanensis

Six new taxoids, taxuyunnanines W (1), X (2), Y (3), Z (5), 10-deacetyl-10-(β-glucopyranosyl)-yunnanxane (8), and 7-(β-xylosyl)-N-methyl-taxol C (10), as well as taxuchin B (4) and yunnanxane (7), have been isolated from the bark of Taxus yunnanensis. Compounds 1 and 2 were characterized as 11(15→1)-abeo taxoids containing an orthoester group, which have not been reported from any Taxus plants to date; isolates 3 and 5 are the examples of taxanes having a tetrahydronfuran ring, being reported only for the second time; and 8 is the first natural 6/8/6 skeletal type taxane glucosidic form. This is also the first report of a co-occurrence of xylosidation and N-methylation in a taxane (10). Compound 4 is the only known chlorine-containing taxane found in nature thus far, and is being reported from this plant for the first time. The structures were determined by spectroscopic and chemical means including 1D and 2D NMR spectra.     

Alkaloids from alkaloids: total synthesis of (±)-7a-epi-hyacinthacine A1 from Z-protected tropenone via Baeyer-Villiger oxidation

Baeyer-Villiger oxidations of several tropane derivatives have been investigated. Whereas tropenones 15a-c underwent exclusive epoxidation to 21a-c, the corresponding 6-oxotropane derivative 28 yielded the desired lactone 29. Baeyer-Villiger oxidation was also possible for the O-isopropylidene-protected diols 32a,b. The resulting lactones 33a,b were employed in the total synthesis of (±)-7a-epi-hyacinthacine A₁ (7a-epi-7) via an intramolecular nucleophilic alkyllithium addition to a carbamate as the key lactamization step. The target compound was prepared from tropenone 15b in 10 steps and 14% overall yield. Enzymatic resolution of pyrrolidine (±)-36 provided a formal total synthesis to both enantiomers of 7.     

Synthesis and chemistry of tricyclic cyclopropene-tricyclo[3.2.2.0]nona-2(4),6-diene

The 1,2-bridged tricyclic cyclopropene, tricyclo[3.2.2.0^2,4]nona-2(4),6-diene (1), has been synthesized by the elimination of 2-bromo-4-chlorotricyclo[3.2.2.0^2,4]-non-6-ene (5). Cyclopropene 1 will undergo different isomerizations in ether solution and in neat conditions. Compound 1 rearranged to an anti-Bredt compound 4 via diradical mechanism in ether and tricyclic compound 6 via vinyl carbene mechanism in neat conditions. Compound 1 can be trapped with DPIBF at different temperatures yielding different results: the exo-endo adduct 2 (exo-addition from the view of the cyclopropene and endo-addition from the view of bicyclo[2.2.2]octene) is a sole product at 0°C by slowly addition of methyllithium, and the exo-endo adduct 2, endo-endo adduct 9, anti-Bredt adduct 3, and styrene 8 are isolated at ether refluxing temperature. Styrene 8 is proposed to be formed from endo-endo adduct 9 by diradical mechanism. The chemistry of exo-endo adduct 2 and endo-endo adduct 9 is as well studied. The exo-endo adduct 2 undergoes hydration in trifluoroacetic acid to generate 1,3-cis-diol 11 followed by eliminations of water and formaldehyde to give naphthalene 12. The endo-endo adduct 9 reacts with water in tetrahydrofuran-containing silica gel to yield 1,4-cis-diol 10. Both 9 and 10 react with trifluoroacetic acid to form trans-3-hydroxy trifluoroacetate 13. Compound 13 will undergo hydrolysis and isomerization to generate 1,3-cis-diol 11 in trifluoroacetic acid.     

Surface plasmon resonance detection of oligonucleotide sequences of the rpoB genes of Mycobacterium tuberculosis

Oligonucleotide sequences related to the normal and mutated rpoB genes of Mycobacterium tuberculosis are detected using a surface plasmon resonance (SPR) biosensor system. A bioselective element was prepared by immobilizing the thiol-modified oligonucleotides of the selected sequence (the capture probe P2) that contains the mutated TCG → TTG codon 531 (evoking drug resistance) of the rpoB gene of M. tuberculosis on a gold sensor surface. Specific hybridization between immobilized probe P2 and complementary target T2 gave the highest sensor response, single-base mismatched oligonucleotide TN (corresponding to the normal gene sequence) produced somewhat smaller response and no response was observed at injection of noncomplementary oligonucleotide TC. The P2-T2 hybridization efficiency is calculated ca. 30% (5 × 10¹² molecules cm⁻²), and the lowest detection limit of T2 was 10 nM. An extended T2E oligonucleotide sequence consisting of T2 sequence and additional 24 nucleotides was shown to cause more pronounced sensor response (at least 5 nM T2E was easily detected). Injection into the sensor cell of the oligonucleotides complementary to the free additional part of T2E after P2-T2E hybridization gave a significant additional SPR response, thus showing that the sandwich hybridization format further improves the sensor sensitivity and decreases the lowest detection limit. The experimental results on surface hybridization between the studied oligonucleotides were in good agreement with thermodynamic parameters of the hybridization calculated for solution conditions. The described approach could be proposed as a basis for creating a biosensor for real-time and label-free diagnostics of drug resistant tuberculosis.     

Synthesis of furan 4′-thio-C-nucleosides, their methylsulfonium and sulfoxide derivatives. Evaluation as glycosidase inhibitors

A series of furan C-nucleosides having a sulfur atom in the sugar ring were synthesised. The α and β anomers of 3-ethoxycarbonyl-2-methyl-5-(4′-thio-d-erythrofuranosyl)furans 10 and 11 were obtained by acid treatment of (4′-S-acetyl-4′-thio-d-arabino-tetritol-1-yl)furan 9. Oxidation of 10 with m-chloroperbenzoic acid gave sulfoxide 12 as one epimer at the sulfur atom whereas 11 was transformed into sulfoxide 13 as an epimeric mixture. S-Methylation of 10 and 11 with methyl triflate led to sulfonium salts 14 and 15. The prepared compounds were found to be moderate inhibitors of α-l-fucosidase.     

Methylene-2-ethynylcyclopropanes: synthesis and biological activity of (Z)- and (E)-9-{[2-ethynyl-2-(hydroxymethyl)cyclopropylidene]methyl}adenine and -guanine

Synthesis of methylene-2-ethynylcyclopropane analogues of nucleosides 12a, 12b, 13a, and 13b is described. Ethyl methylenecyclopropane carboxylate 14 was hydroxymethylated to give alcohol 15, which was reduced to diol 16. Selective protection with tert-butyldimethylsilyl group gave derivative 17, which was oxidized to aldehyde 18. Wittig reaction with CBr₄ gave dibromoalkene 19. Elimination of both bromine atoms afforded methylene-2-ethynylcyclopropane 20. Bromoselenenylation using N-bromosuccinimide and diphenyldiselenide gave intermediate 21. Alkylation of adenine and 2-amino-6-chloropurine with 21 provided the Z,E-isomeric mixtures 22a and 22c. Oxidation afforded selenoxides 23a and 23c. Mild thermolysis furnished methylenecyclopropanes Z-24a, E-24a, and 24c. Deprotection and separation of Z,E-isomers gave adenine analogues 12a and 13a, and 2-amino-6-chloropurine intermediates 12c and 13c. Hydrolytic dechlorination of 12c and 13c afforded guanine analogues 12b and 13b. Adenine Z-isomer 12a inhibits replication of Epstein-Barr virus through its cytotoxicity. The E-isomer 13a is a substrate for adenosine deaminase.     

New phlegmarane-type, cernuane-type, and quinolizidine alkaloids from two species of Lycopodium

Two new phlegmarane-type alkaloids, cermizines A (1) and B (2), three new quinolizidine alkaloids, cermizine C (3) and senepodines G (4) and H (5), and a new C₁₆N₂ type alkaloid consisting of a quinolizidine and a piperidine ring, cermizine D (6), as well as two new cernuane-type alkaloids, cernuine N-oxide (7) and lycocernuine N-oxide (8), have been isolated together with cernuine (9) and lycocernuine (10) from the club moss Lycopodium cernuum and L. chinense. The relative stereochemistry of 1-4 and 6, and the absolute stereochemistry of 5, 7, and 8 were elucidated by combination of NOESY correlations, modified Mosher's method, chemical transformations, and computational methods. Cermizine D (6) might be a biosynthetic intermediate of cernuane-type alkaloids such as 7-10.     

Regioselective synthesis of 3,4,6,7-tetrahydro-3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones through ascorbic acid catalyzed three-component domino reaction

An efficient, three-component domino reaction of dimedone 1, aromatic aldehydes (2a–o), and 1,3-cyclohexanedione 1a in the regio-selective synthesis of 3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones (3a–o) is reported. The desired product, 3 is efficiently promoted by ascorbic acid as an organo catalyst.