Isolation of a new indoxyl alkaloid,Amoenamide B,from Aspergillus amoenus NRRL 35600: Biosynthetic implications and correction of the structure of Speramide B

A new prenylated indoxyl alkaloid, Amoenamide B (1), was isolated from Aspergillus amoenus NRRL 35600 along with Asperochramide A (2). Although many prenylated oxindole alkaloids, containing bicyclo[2.2.2]diazaoctane cores, have been isolated from the fungus of the genera Aspergillus and Penicillium to date, 1 is the fourth compound with the indoxyl unit containing the cores. During the structure elucidation of 1, we found that the planar structure matched to that of Speramide A (3), isolated from A. ochraceus KM007, but the reported structure of 3 was incorrect and turned out to be that of Taichunamide H (4), recently isolated from A. versicolor HDN11-84.     

Hydrogen-bond-assisted supramolecular 1-D tape-like structures of mesogenic bis-pyrazoles

Two new series of isomeric bis-pyrazoles 1a–b are prepared, characterized, and their mesomorphic properties investigated. These pyrazoyl derivatives were obtained from the condensation of α,β-diketones 2a–b with hydrazine monohydrate in refluxing THF. Two single crystallographic structures of compounds mesogenic 1a (n=14) and nonmesogenic 1b (n=8) were determined by X-ray analysis. Both 1a–14 and 1b–8 crystallize in a triclinic space group P?1 and monoclinic C2/c group, respectively. An extended H-bonded structure was formed in both crystal lattices, giving a pseudo 1D-polymeric tape-like structure. Derivatives 1a exhibited smectic A/C mesophases, in contrast, derivatives 1b were all nonmesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation and the coplanarity of the five rings over than in 1a. The correlation between the molecular structures and the mesomorphic properties is discussed.     

Deboronation-induced ratiometric emission sensing of fluoride by 1,3,5-tris-(o-carboranyl-methyl)benzene

1,3,5-Tris-(o-carboranyl-methyl)benzene (closo-1) and its nido-form (nido-1) were synthesized and fully characterized. The solid-state molecular structure of closo-1 was determined by single-crystal X-ray diffraction analysis. Compound closo-1 exhibited an intense single emission in various organic solvents that was red-shifted with increasing solvent polarity. The positive solvatochromic effect and theoretical calculation results at the first excited (S₁) optimized structure of closo-1 strongly suggest that this emissive band can be assigned to an intramolecular charge transfer. Meanwhile, nido-1 showed a pronounced red-shift of the emissive band compared to that of closo-1 and aroused low-energy emission. The specific emissive features of nido-1 were attributed to the elevation of its HOMO level, estimated by cyclic voltammetry. The photophysical changes by conversion from closo-1 to nido-1 allowed the emissive color-tunable sensing of fluoride. Thus, the tris-o-carboranyl compound showed great potential as a chemodosimeter for fluoride anion sensing, detectable by the naked-eye.     

Verbenanone,an octahydro-5H-chromen-5-one from a Hawaiian-plant associated fungus FT431

Verbenanone (1), a new secondary metabolite with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.     

Non-terpenoid C-15 metabolites from the red seaweed Laurencia pinnatifida

The structures of absolute configurations of the halogenated vinyl acetylenes which are natural products from the red alga Laurencia pinnatifica (Gmal. Lamour) are described. The structure of trans- pinnatifidenyne 2 was determined by spectral, chemical and X-ray diffraction analyses. The structure of cis-pinnatifidenyne 1 is based on spectral comparison and chemical interconversion with the trans-isomer 2. The structure of the acyclic trienyne 8 was secured as: (6R,7R)-3-cis, 9-cis,12-cis,6-acetoxy,7-chloropentadeca-3,9,12-trien-1-yne by synthesis from cis-pinnatifidenyne 1. The reactivity of these compounds to various conditions of catalytic hydrogenation has been examined in detail.     

The configuration and conformation of isogermacrone. The significance of crossed conformations in olefinic cyclisations

The 9,10-double bond of isogermacrone was assigned the Z configuration based on¹HNMR nOe measurements and the ¹³CNMR shifts of the methyl groups. An X-ray crystal structure determination verified this conclusion and the structure of isogermacrone was shown to be (2Z, 7E)-3,7-dimethyl-10(1-methylethyl-idene)-2,7-cyclodecadien-1-one (1). The molecule crystallised in an anti conformation, which according to ¹HNMR is the predominant conformation in solution at room temperature.¹H NMR spectroscopy revealed the presence of syn and anti conformers in the ratio 1:2 at about -60°. The stereochemistry of the base-induced formation of isogermacrone 1 from germacrone 2 and that of the transannular cyclisation of isogermacrone are discussed.     

Halichonic acid,a new rearranged bisabolene-type sesquiterpene from a marine sponge Halichondria sp.

A new compound, halichonic acid (1), was isolated from a marine sponge Halichondria sp., together with (6R,7S)-7-amino-7,8-dihydro-α-bisabolene (2). The structure of 1 was elucidated by spectroscopic analysis and ECD spectrum calculation to be a rearranged bisabolene-type sesquiterpene having a 3-azabicyclo[3.3.1]nonene moiety. Compound 2 was cytotoxic against HeLa cells with an IC₅₀ value of 50?μM, whereas 1 did not show cytotoxicity even at 50?μM. It is possible that 1 is biosynthesized from farnesyl pyrophosphate and glycine, with rearrangement.     

Isolation of (E)-9,10-dihydroxy-2-decenoic acid from royal jelly and determination of the absolute configuration by chemical synthesis

(E)-9,10-Dihydroxy-2-decenoic acid 1 was isolated as a new compound from royal jelly. The planar structure was deduced by spectroscopic analyses, whereas the absolute configuration was established by chemical synthesis of both enantiomers of 1. The natural product was revealed to be ca. 3.5:1 mixture of (R)- and (S)-acids by comparison of 1 with authentic samples.     

Naturally-occurring acetylenic compounds and derivatives : Regio- and stereocontrolled chloroformylation of 2-(1-propynyl)thiophene and 2-phenyl-5-(1-propynyl)thiophene

2-Phenyl-5-(1-propynyl)thiophene (1), isolated from Coreopsis grandiflora, and 2-(1-propynyl)thiophene (5), an immediate precursor in the synthesis of junipal (2), were synthesized in high yield by a Pd-catalyzed reaction between propyne and 2-iodo-5-phenylthiophene (4) or 2-iodothiophene (6), respectively. Reaction of 5 with the Vilsmeier reagent derived from POCl₃ and N-methylformanilide (MFA) afforded a mixture from which it was possible to isolate (E)-3-chloro-2-methyl-3-(2-thienyl)acrolein (10) in 37.7% yield. The structure and stereochemistry of 10 was unequivocally established by X-ray diffraction of a single crystal of the 2,4-dinitrophenylhydrazone of 10. GLC analysis showed that 10 was contaminated by ca 7% with an isomer to which, on the basis of ¹H-NMR and mass spectra, the structure of (Z)-3-chloro-2-methyl-3-(2-thienyl)acrolein (11) was attributed.Contrary to what was expected from the literature, junipal (2) represented only a minor component in the reaction mixture obtained by the Vilsmeier reaction on 5.Reaction of 1 with POCl₃ and MFA afforded (44.6% yield) a (E)-3-chloro-2-methylacrolein to which the structure 15 was attributed. Compound 15 was also contaminated by ca 10% of an isomer 16, which very probably corresponded to the (Z)-stereoisomer of 15.     

Iridoids in equatorial and tropical flora—III : Isolation and partial synthesis of 6-epiaucubin a new glucosidic iridoid

The structure of a new glucosidic iridoid, 6-epiaucubin 1, isolated from leaves of a tropical tree, Tecoma chrysantha Jacq., was established by analysis of the spectroscopical data of 1 and its hexa-O-acetyl derivative 3. Partial synthesis of 1 from its epimer, aucubin 2, is also reported.     

Antimicrobial constituents of the sponge siphonodictyon coralliphagum

The burrowing sponge Siphonodictyon coralliphagum contains two phenolic aldehydes, siphonodictyal-A (1) and siphonodictyal-B (2). The structure of siphonodictyal-A (1) was determined by interpretation of spectral data and the synthesis of a derivative. The structure of siphonodictyal-B (2) resulted from interpretation of spectral data and the synthesis of a degradation product. Both compounds exhibit antimicrobial activity.     

The structures of evonine and neoevonine alkaloids obtained from Euonymus Sieboldiana blume

Evonine (1) and neoevonine (2) were isolated from Euonymus Sieboldiana Blume. The structural studies of the principal alkaloid, evonine were carried out extensively by chemical and spectroscopic methods, resulting in the establishment of the structure of the alkaloid as 1: it is a highly oxygenated sesquiterpene of eudesman type, which is esterified with five moles of acetic acid and evoninic acid (33). The derivatives for the structure determination of 1 are summarized in Charts I–III. Interconversion of the two alkaloids, (1 and 2) was achieved and the structure of neoevonine was elucidated as 2.     

Enantiopure erythro- and threo-1-aryl-1-[2-pyrrolidyl]-methanols: synthesis from l-proline

Enantiopure (1R,2S)-erythro- and (1S,2S)-threo-isomers of four new aryl-pyrrolidyl alcohols 5aH, 5aMe, 5bH and 5bMe have been obtained in five steps from (−)-(S)-proline and fully characterized. The oxidation of alcohol 8 into aldehyde 9 was the most difficult step and racemization occurs during Swern oxidation but this difficulty can be overcome by using SO₃/pyridine as oxidant. Diastereomer I of the protected amino alcohol 10a crystallized and was shown to be the (1R,2S)-erythro-isomer (e-10a-I) using X-ray crystallography. Therefore the (1R,2S)-erythro structure was assigned to all compounds obtained from e-10a-I, and, as a consequence, the (1S,2S)-threo structure was assigned to diastereomers II.     

Three new vinyl acetylenes from the marine red alga laurencia

The structures of three new halogenated vinyl acetylenes are described which are natural products from various species of the red seaweed Laurencia. The structure of chlorofucin (1) isolated from Laurencia snyderae was determined by X-ray diffraction analysis. Poiteol (2) was isolated from Laurencia poitei and its structure was also determined by single crystal X-ray diffraction experiments. The structure of obtusenyne (3) was based on a combination of chemical and spectral methods. The ¹³C NMR spectra of these new compounds are presented and assignments made.     

Development of a light-up fluorescent probe for HRAS G-quadruplex DNA

The development of small-molecule G-quadruplex DNA probes has attracted significant attention in recent years. However, G-quadruplexes can display a wide variety of topologies, which process different structures and functions. Therefore, selective discrimination one G-quadruplex structure over another is promising. Herein, we reported the design, synthesis and biological evaluation of a long-chain fatty amine functionalized triphenylamine-quinolinium conjugate 1b. Significant enhancement of the fluorescence intensity (over 180 fold) was observed when 1b bound with HRAS G-quadruplex DNA, while much weaker enhancements were presented in the presence of other G-quadruplexes (45–90-fold) and single/double-stranded DNAs (less than 20-fold), indicating 1b had an excellent selectivity to HRAS. The details of the interactions were investigated by UV–Vis, FID and CD analysis. The results show 1b could interact and stabilize HRAS structure mainly by π-π stacking binding mode. The introduced amine chain of the structure core was found to be better in the terms of inducing selectivity toward G-quadruplex structure. In addition, the application of 1b as a fluorescent agent for living cell imaging was also demonstrated.     

Turtschamide,a cytotoxic putrescine bisamide from Corydalis turtschaninovii

A putrescine bisamide with a unique cyclic structure derived from l-tyrosine, turtschamide (1), was isolated from the tubers of Corydalis turtschaninovii. The structure of 1 was established by extensive spectroscopic study, and its absolute configuration was determined by a combination of NOE experiment and application of the Marfey’s method. Turtschamide (1) exhibited cytotoxicity against the A549, SK-OV-3, SK-MEL-2, and HCT-15 cells.     

Sarcophine,a new epoxy cembranolide from marine origin

From the soft bodied coral Sarcophytum glaucum a crystalline compound-sarcophine (1), which is believed to be one of the repellents protecting the coral against predators, was isolated. The functional groups of 1 have been deduced from detailed NMR study and the whole molecular structure has been determined by a single-crystal 3-dimensional X-ray diffraction study proceeding from direct methods. The compound crystallizes in orthorhombic crystals, space group P2₁2₁2₁, and there are four molecules in each unit cell of dimensions a = 12·429(3), b = 13·766(3) and c = 10·750(1). The structure was found to be a new epoxy cembranolide. The mass spectrum and CD of 1 and several simple derivatives as well as the conformation of 1 in solution are discussed.     

Structure,chemistry and stereochemistry of rastevione,a sequiterpenoid from the genus stevia

The structure and relative stereochemistry of rastevione (1a), the main constituent of the roots of S. serrata and S. rhombifolia, were deduced from chemical transformations combined with spectral data and by a single crystal X-ray diffraction study of rastevione acetate (1b). Chemical correlation of a rastevione derivative with a molecule thought to have structure IVb, suggests the structures of several previously described longipinene and longipinane derivatives, should be revised. The behaviour of longipinane-7α,8β,9β-triol-l-one in the presence of periodic acid was studied, and the structure of the reaction product established from deuterium labeling experiments showed the 7α,8β diol split.     

Norcrocrassinone: A novel tetranorditerpenoid possessing a 6/6/5 fused ring system from Croton crassifolius

Norcrocrassinone (1), a novel tetranorditerpenoid possessing a fused 6/6/5 ring system, was isolated from the roots of Croton crassifolius. The structure of 1 was elucidated by extensive spectroscopic methods and confirmed by single crystal X-ray diffraction. The anti-Alzheimer’s disease (AD) activity of 1 was evaluated using humanized Caenorhabditis elegans AD pathological model.     

Crystal and molecular structure of the levorotatory (1R,2S)-ephedrinium (S)-t-butylsulfinylacetate: a definitive proof of the absolute configuration of enantiomeric t-butyl methyl sulfoxides

The levorotatory enantiomer of t-butylsulfinylacetic acid 3 was obtained in the reaction of the α-carbanion of (+)-t-butyl methyl sulfoxide 1 with carbon dioxide. The same enantiopure form of the acid 3 was isolated from its diastereomerically pure levorotatory salt 5 with (−)-(1R,2S)-ephedrine. The structure of this salt was determined by X-ray analysis and the absolute configuration (S) at sulfur was ascribed to the t-butylsulfinylacetate anion. Consequently, the absolute configuration (S) was assigned to the acid (−)-3 and its precursor (+)-t-butyl methyl sulfoxide 1.