Total synthesis of (+)-massarinolin B and (+)-4-epi-massarinolin B, fungal metabolites from Massarina tunicata

The Cr(II)- and Ni(II)-mediated coupling of several tricyclic chiral aldehydes with (E)-β-iodomethacrylates (Nozaki-Hiyama-Kishi reaction) was successfully applied to the preparation of some valuable key intermediates of our synthetic strategy to the fungal metabolites (+)-massarinolin B, (+)-4-epi-massarinolin B and (+)-massarinolin C.     

Asymmetric syntheses of (+)-negamycin, (+)-3-epi-negamycin and sperabillin C via lithium amide conjugate addition

The chemo- and enantioselective reduction of ethyl 4-chloroacetoacetate and the diastereoselective conjugate addition of enantiopure lithium N-benzyl-N-(α-methylbenzyl)amide to an α,β-unsaturated ester have been used as the key steps in the total asymmetric syntheses of (+)-negamycin (in 13 steps and 24% overall yield), (+)-3-epi-negamycin (in 13 steps and 10% overall yield) and sperabillin C (in 17 steps and 13% overall yield) from commercially available starting materials.     

Biotransformation of (+)-(1R,2S)-fenchol by the larvae of common cutworm (Spodoptera litura)

Biotransformation of (+)-(1R,2S)-fenchol by the larvae of Spodoptera litura was carried out. Substrate was converted to three new terpenoids, (+)-(1R,2S)-10-hydroxyfenchol, (+)-(1R,2R,3S)-8-hydroxyfenchol and (−)-(1S,2S,6S)-6-exo-hydroxyfenchol, and one known terpenoid, (−)-(1R,2R,3R)-9-hydroxyfenchol. These structures were established by NMR, IR, specific rotation and mass spectral studies.     

Stereoselective synthesis of tetrahydroisoquinoline alkaloids: (−)-trolline, (+)-crispin A, (+)-oleracein E

Tetrahydroisoquinoline alkaloids, (S)-(−)-trolline, (R)-(+)-crispin A, and (R)-(+)-oleracein E, have been synthesized stereoselectively from the both enantiomers of common intermediate (S)-4 and (R)-4. The key step in the synthesis include a stereoselective Bi(OTf)₃-catalyzed intramolecular 1,3-chirality transfer reaction of chiral non-racemic amino allylic alcohols (S)-6 and (R)-6 to construct both enantiomers of (E)-1-propenyl tetrahydroisoquinoline 4.     

Chiral self-assembly of triorganotin complexes: Syntheses, characterization, crystal structures and antitumor activity of organotin(IV) complexes containing (R)-(+)-methylsuccinic acid, (S)-(+)-methylglutaric acid and l-(−)-malic acid ligands

Six new chiral triorganotin(IV) complexes, {(R₃Sn)₂[C₃H₆(COO)₂]}_n (R = Me: 1; Bu: 2), {(R₃Sn)₂[C₄H₈(COO)₂]}_n (R = Me: 3; Bu: 4), and {(R₃Sn)₂[C₂H₄O(COO)₂]}_n (R = Me: 5; Bu: 6) have been prepared by treatment of (R)-(+)-methylsuccinic acid, (S)-(+)-methylglutaric acid and l-(−)-malic acid, with the corresponding R₃SnCl (R = Me, Bu) and sodium ethoxide in methanol. All the complexes were characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy and TGA. Except for 3, all of the complexes were also characterized by X-ray crystallography. The structural analyses reveal that complexes 1 and 5 have 2D network structures in which (R)-(+)-methylsuccinic acid and l-(−)-malic acid act as tetradentate ligands coordinated to trimethyltin(IV) ions. Complexes 2 and 4 have 3D metal-organic framework structures in which the deprotoned acids serve as tetradentate ligands. Complex 6 adopts a 1D zigzag chain structure and forms a 2D supramolecular framework through intermolecular C-H?O interactions. In addition, the antitumor activities of complexes 1-6 have been studied. We also have measured the specific rotation of the chiral dicarboxylic acids and the organotin derivatives.     

Synthesis of the dopamine D2/D3 receptor agonist (+)-PHNO via supercritical fluid chromatography: preliminary PET imaging study with [3-C]-(+)PHNO

Carbon-11 labeled (+)-4-[1-¹¹C]propyl-3,4,4a,5,6,10b-hexahydro-2H-naphtho[1,2-b][1,4]oxazin-9-ol ([1-¹¹C]-(+)-PHNO) is a dopamine D₃-preferring agonist radiopharmaceutical used for medical imaging by positron emission tomography (PET). We report the synthesis of (+)-PHNO using supercritical fluid chromatography for enantiomeric resolution of its norpropyl derivative, HNO, followed by propylation. (+)-HNO was used to prepare the radiolabeling precursor, (+)-trans-4-acetyl-9-triisopropylsilyloxy-2,3,4a,5,6,10b-hexahydro-4H-naphth[1,2b][1,4]oxazine, in 12 steps. Modifications to the labeling procedure were made to ensure consistent preparation of [3-¹¹C]-(+)-PHNO via [¹¹C]CH₃I. A preliminary PET imaging study was carried out with this tracer in an attempt to image dopamine receptors in brown adipose tissue (brown fat) in vivo.     

Chemo-enzymatic enantio-convergent asymmetric synthesis of (R)-(+)-Marmin

Asymmetric biohydrolysis of trisubstituted terpenoid oxiranes (rac-1a-rac-3a) was accomplished by employing the epoxide hydrolase activity Rhodococcus and Streptomyces spp. Depending on the biocatalyst, the biohydrolysis proceeded in an enantio-convergent fashion and gave the corresponding vic-diols in up to 97% ee at conversions beyond the 50%-threshold. In order to avoid a depletion of the ee of product by further oxidative metabolism, bioconversions had to be conducted in an inert atmosphere with exclusion of molecular oxygen. The synthetic applicability of this method was demonstrated by the asymmetric total synthesis of the monoterpenoid coumarin (R)-(+)-Marmin in 95% ee.     

Copper mediated scalemic organolithium reagents in alkaloid syntheses

Scalemic 2-pyrrolidinylcuprates generated via asymmetric deprotonation of N-Boc-pyrrolidine followed by treatment with THF soluble CuCN·2LiCl react with ω-functionalized vinyl halides to afford 2-alkenyl-N-Boc-pyrrolidines. N-Boc deprotection and cyclization via intramolecular N-alkylation generates the pyrrolizidine or indolizidine skeletons. Subsequent functional group manipulation affords enantioenriched (+)-heliotridane, (+)-isoretronecanol, a formal synthesis of (+)-laburnine, (+)-(R)-2,3,5,7a-tetrahydro-1H-pyrrolizine, (R)-1,2,3,5,6,8a-hexahydroindolizine, (+)-ent-δ-coniceine, (+)-tashiromine and (+)-5-epitashiromine.     

Interaction of (+)-Strebloside and Its Derivatives with Na+/K+-ATPase and Other Targets

Docking profiles for (+)-strebloside, a cytotoxic cardiac glycoside identified from Streblus asper, and some of its derivatives and Na⁺/K⁺-ATPase have been investigated. In addition, binding between (+)-strebloside and its aglycone, strophanthidin, and several of their other molecular targets, including FIH-1, HDAC, KEAP1 and MDM2 (negative regulators of Nrf2 and p53, respectively), NF-κB, and PI3K and Akt1, have been inspected and compared with those for digoxin and its aglycone, digoxigenin. The results showed that (+)-strebloside, digoxin, and their aglycones bind to KEAP1 and MDM2, while (+)-strebloside, strophanthidin, and digoxigenin dock to the active pocket of PI3K, and (+)-strebloside and digoxin interact with FIH-1. Thus, these cardiac glycosides could directly target HIF-1, Nrf2, and p53 protein–protein interactions, Na⁺/K⁺-ATPase, and PI3K to mediate their antitumor activity. Overall, (+)-strebloside seems more promising than digoxin for the development of potential anticancer agents.     

Analysis of the major chiral compounds of Artemisia herba-alba essential oils (EOs) using reconstructed vibrational circular dichroism (VCD) spectra: En route to a VCD chiral signature of EOs

An unprecedented methodology was developed to simultaneously assign the relative percentages of the major chiral compounds and their prevailing enantiomeric form in crude essential oils (EOs). In a first step the infrared (IR) and vibrational circular dichroism (VCD) spectra of the crude essential oils were recorded and in a second step they were modelized as a linear weighted combination of the IR and VCD spectra of the individual spectra of pure enantiomer of the major chiral compounds present in the EOs. The VCD spectra of enantiomer of known enantiomeric excess shall be recorded if they are not yet available in a library of VCD spectra. For IR, the spectra of pure enantiomer or racemic mixture can be used. The full spectra modelizations were performed using a well known and powerful mathematical model (least square estimation: LSE) which resulted in a weighting of each contributing compound. For VCD modelization, the absolute value of each weighting represented the percentage of the associate compound while the attached sign addressed the correctness of the enantiomeric form used to build the model. As an example, a model built with the non-prevailing enantiomer will show a negative sign of the weighting value. For IR spectra modelization, the absolute value of each weighting represented the percentage of the compounds without of course accounting for the chirality of the prevailing enantiomers. Comparison of the weighting values issuing from IR and VCD spectra modelizations is a valuable source of information: if they are identical, the EOs are composed of nearly pure enantiomers, if they are different the chiral compounds of the EOs are not in an optically pure form. The method was applied on four samples of essential oil of Artemisia herba-alba in which the three major compounds namely (−)-α-thujone, (+)-β-thujone and (−)-camphor were found in different proportions as determined by GC–MS and chiral HPLC using polarimetric detector. In order to validate the methodology, the modelization of the VCD spectra was performed on purpose using the individual VCD spectra of (−)-α-thujone, (+)-β-thujone and (+)-camphor instead of (−)-camphor. During this work, the absolute configurations of (−)-α-thujone and (+)-β-thujone were confirmed by comparison of experimental and calculated VCD spectra as being (1S,4R,5R) and (1S,4S,5R) respectively.     

Stereoconvergent preparation of chiral vinylsilanes by cuprate substitution of α-acetoxyallylsilanes. Application to the synthesis of (S)-(+)-bishomomanicone

Enantiomerically enriched (E)- and (Z)-configured α-acetoxyallylsilanes have been prepared starting from a chiral acylsilane bearing an asymmetric unit at the silicon portion. Treatment of these compounds with organocuprates afforded the respective vinylogous substitution products in high yields and high stereoselectivities. The transformations proceed essentially by complete anti attack of the nucleophiles to the allylic acetates and predominantly via transition states leading to the (E)-configured vinylsilane products. By the proper choice of the double bond geometry in the starting material, the configuration of the newly formed stereogenic center can be controlled. The method represents a new and flexible entry into chiral vinylsilanes that can be used for subsequent transformations. As an example, the α,β-unsaturated γ-chiral, naturally occurring ketone (S)-(+)-bishomomanicone was synthesized with this method, which represents the first synthetic access to this compound.     

Stereoselective synthesis of (+)-(8R,8aR)-perhydro-8-indolizidinol

A highly stereoselective total synthesis of (+)-(8R,8aR)-perhydro-8-indolizidinol is described. Key steps involved in this synthesis are diastereoselective zinc allylation, azido-olefin cyclization and reductive amination followed by cyclization which effectively constructed the indolizidine ring. This contributes a unique approach to the synthesis of indolizidine alkaloids that offers the advantages of brevity and relatively high overall yields.     

New synthetic approach to substituted isoindolo[2,1-a]quinoline carboxylic acids via intramolecular Diels-Alder reaction of 4-(N-furyl-2)-4-arylaminobutenes-1 with maleic anhydride

Acylation of substituted 4-(furyl-2)-4-arylaminobut-1-enes with maleic anhydride provided 2-allyl-6-carboxy-4-oxo-3-aza-10-oxatricyclo[5.2.1.0^1,5]dec-8-enes in high yield under mild reaction conditions. The Diels-Alder adducts are formed via an initial amide formation followed by a stereoselective intramolecular [4+2] exo-cycloaddition reaction. Treatment of the tricyclic compounds with phosphoric acid at high temperatures (70-120 °C) promoted cyclic ether opening, intramolecular cyclization and aromatization to give the corresponding tetracyclic compounds, 5,6,6a,11-tetrahydro-10-carboxyisoindolo[2,1-a]quinolines, in moderate yields. The influence of the acid and the reaction temperature on the cyclization reactions are also discussed.     

Synthesis of enantiomericcis-homocaronic acids from (+)-3-carene

The syntheses of the dimethyl ester of (-)-(1R)-cis-homocaronic acid (7 steps, overall yield 43 %) and its antipode, the dimethyl ester of (+)-(1S)-cis-homocaronic acid (5 steps, overall yield 27 %), were performed starting from (+)-3-carene and its derivatives, (+)-4-acetyl-2-carene and (+)-4-acetoxymethyl-2-carene. Oxidative cleavage in the key stages was carried out by ozonization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 314–318, February, 1995.     

Sedum alkaloids—VII : Structure and synthesis of (+)-4-hydroxysedamine and (+)-4-hydroxyallosedamine

The structures of (+)-4-hydroxysedamine ¹ and (+)-⁴-H-hydroxyallosedamine ², two new minor alkaloids from Sedum itacre, are reported 1 and 2 were synthesized, and their absolute configuration established, via the optically pure tetrahydro 1,3-oxazines 17 and 18.     

Synthesis, stereochemical and conformational properties of trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-one oxime ethers

A convenient synthesis and structural characterization of (Z)- and (E)-trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-one oxime ethers has been achieved. By analysis of vicinal interproton coupling constants, it is believed that trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-ones which exist predominantly in the diequatorial half-chair or sofa conformation was found to exist predominantly in the diaxial orientation upon conversion to the corresponding oxime ether derivatives.     

Crosslinking and ageing of C labelled polyisoprene part 1: Synthesis and polymerisation of 4-C-isoprene

4-¹³C-isoprene was prepared by the Wittig reaction. All reaction steps were optimised using unlabelled compounds. By reaction with triphenyl phosphine, ¹³C labelled methyl iodide afforded labelled methyl-triphenyl phosphine iodide in 84% yield. This reacted with meth acrolein with production of 4-¹³C-isoprene in 64% yield. Labelled polyisoprene was prepared by anionic polymerisation initiated by t-butyl lithium. Based on ¹³CH₃I the overall yield is ca 30%. The polymer was characterized by ¹H and ¹³C NMR spectroscopy. The contribution of each microstructure was [cis 1-4, 72%]; [trans 1-4, 10%]; [3-4, 18%].     

Structure and redox behavior of Ru(II)-diene complexes

A series of Ru(acac)₂(η⁴-diene) complexes containing cis- and trans-diene coordination have been investigated by cyclic voltammetry to correlate structural bonding and conformation patterns of diene ligands with redox behaviors. The solid-state structure of Ru(acac)₂(2,3-dimethyl-1,3-butadiene) has been determined by single crystal X-ray diffraction methods. Ru(acac)₂(2,3-dimethyl-1,3-butadiene) crystallizes in the monoclinic space group C2/c with a = 12.368(2) Å, b = 17.0600(2) Å, c = 16.0110(2) Å, β = 98.4405(10)° and V = 3341.38(10) ų for Z = 8. A structural comparison between several Ru-trans-η⁴-diene complexes and Ru-η⁴-1,3-cyclohexadiene revealed no difference in the Ru-C(diene) bond distances. However, through cyclic voltammetry experiments these species demonstrated different redox behavior, as function of the coordinated diene ligand.     

Synthesis of Δ-15-deoxy-PG-J1 methyl ester and epi-Δ-15-deoxy-PG-J1

The synthesis of racemic Δ^12,14-15-deoxy-PG-J₁ is readily achieved in six steps employing as the key transformation a one-pot conjugate addition-Peterson olefination sequence using exo-2-trimethylsilyl-3a,4,7,7a-tetrahydro-4,7-methanoinden-1-one. Additionally a Noyori-type three-component coupling approach is employed for the synthesis of enantioenriched epi-Δ¹²-15-deoxy-PG-J₁ from 4(S)-tert-butyldimethylsilyloxycyclopent-2-enone.     

Biotransformation of (+)-isofraxinellone by Aspergillus niger and insect antifeedant activity

The biotransformation of (+)-isofraxinellone (1) by Aspergillus niger was investigated. Compound 1 was transformed to only one new compound 2. The structure of 2 was identified as (-)-(4S)-4-hydroxyisofraxinellone which was regio- and stereo-selective hydroxylated at the C-4 position by IR, EI-MS 1D and 2D NMR. Absolute configuration of hydroxyl group at the C-4 position was detected by modified Mosher’s method. Antifeedant activity of compounds 1 and 2 against larvae of Spodoptera litura was assayed. These compounds showed potent antifeedant activity and ED₅₀ (50% of effective dose) values were 3.91 and 4.43 μg/cm², respectively.