Aufkl?rung der 1H- und 13C-NMR-spektren sowie der kristallstruktur unges?ttigter glycosylphosphonate und konformationsberechnungen an modellen1

By application of a modified LAOCN-3 program a complete elucidation of the ¹H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined ⁿJ(H, H) and novel ⁿJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The ¹³C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as ¹J(C-H) and ⁿJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations ¹J(C-1,H_e)>¹J(C-1, H_a) and ¹J(C-1, P_e) >¹J(C-1, P_a) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects.     

Strukturaufklärung einer neuen diterpensäure aus metasequoia glyptostroboides mit hilfe der 13C-NMR-spektroskopie

In addition to methyl communate (1) the hitherto unknown 3-acetoxylabda-8(20), 13-diene-15-oic acid (3) has been isolated from the autumnal leaves of metasequoia glyptostroboides. Its structure has been determined by ¹³C NMR spectroscopy, aided by the analysis and assignment of the ¹³C NMR spectra of two degradation products as well as of α-onocerine diacetate (13) and of methyl communate (1).     

13C NMR Study of ginseng sapogenins and their related dammarane type triterpenes

In connection with structure studies on dammarane type triterpenes and their glycosides, assignments of ¹³C NMR signals of fifteen 20-hydroxy-dammarane derivatives including Ginseng sapogenins have been achieved by the aid of shift reagents and deuterated compounds. It has been found that the differences of the 17 C, 21 C and 22 C chemical shifts between pairs of C-20 epimers are remarkable especially in the case of 12β-hydroxy derivatives, being significant for the study of the C-20 stereochemistry.     

Six new monoterpenoid indole alkaloids from the aerial part of Gelsemium elegans

Six new monoterpenoid indole alkaloids along with four known analogues were isolated from the aerial part of Gelsemium elegans. Their structures with absolute configurations were elucidated by NMR, HRESIMS, X-ray diffraction, CD spectra, and molecular modeling calculation. Among them, gelselenidine (1) is a new gelsedine-type alkaloid with a 2,3-epoxybutane unit. Gelseziridine (2) is the first example of monoterpenoid indole alkaloids with an oxaziridine residue. Compounds 6 and 7 are a pair of N₄ epimers of humantenine N₄-oxide. A plausible biogenetic pathway for compounds 1-4 was also proposed.     

The pH dependence of phenolphthalein: A 13c NMR study

The pH dependence of the ¹³C NMR spectra of phenolphthalein has been measured and interpreted. The spectrum of the neutral compound 1 is compared with the spectra of the dianion 4, the trianion5 and the carbocation7. At the first time spectroscopic evidence for the carbinol 6 is given.     

Vincamajorines A and B,monoterpenoid indole alkaloids with new carbon skeletons from Vinca major

Two new monoterpenoid indole alkaloids, vincamajorines A (1) and B (2), were isolated from Vinca major. Their structures were elucidated by means of 1D and 2D NMR, and HREIMS spectroscopic data. The relative and absolute configurations were deduced by comparing the experimental ¹³C NMR, ECD spectra, and OR data with those theoretically calculated. Vincamajorine A (1) represents a new C₂₀ carbon skeleton arranged compactly in seven rings, and vincamajorine B (2) is an alkaloid with an unprecedented 6/5/7/5/6 pentacyclic ring system. A possible biosynthetic pathway was also proposed for the formation of 1 and 2.     

Lycogladines A-H,fawcettimine-type Lycopodium alkaloids from Lycopodium complanatum var. glaucum Ching

Five new fawcettimine-type alkaloids (1–5) and three new natural products (6–8), along with four known analogues, fawcettimine (9), fewcettidine (10), lycopoclavamine B (11), and lycopladine B (12), were isolated from the whole plant of Lycopodium complanatum var. glaucum Ching. The structures of lycogladines A-H (1–8) were determined based on HRESIMS, 1D and 2D NMR spectroscopic analysis, as well as single-crystal X-ray diffraction. Compound 1 possesses a new ring system that is formed through the linkage of C-13-OC-2, which is rarely present in Lycopodium alkaloids (LAs). Compounds 1–8 were tested for their β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) and acetylcholinesterase (AChE) inhibitory activities.     

Simple aromatic amines from justicia gendarussa. 13C NMR spectra of the bases and their analogues

Four simple 0-disubstituted aromatic amines have been isolated from the leaves of Justicia gendarussa Burm and characterized as 2-amino benzyl alcohol (3), 2-(2′-amino-benzylamino) benzyl alcohol (4) and their respective 0-methyl ethers 1 and 2 from ¹H NMR and mass spectral analyses of the bases and their acetates. Structures 3 and 4 have also been confirmed by synthesis. Intramolecular hydrogen bonding (cf. 9, 13 and 14) has been envisaged to explain the unexpected shielding of -CH₂-OH carbon signals of 34 on acetylation and upfield displacement of -CH₂-N signal of 2a vs 4a in their ¹³C NMR spectra in CDCl₃ solution ₁J_CH values have been found to be useful for the assignment of aromatic methine carbon signals in o-disubstituted compounds. Part 68 of the series Studies on Indian medicinal plants. For Part 67, see P. K. Dutta, D. Bagchi and S.C. Pakrashi, Indian J. Chem. in press.     

Fluxional behaviour of Rh4(CO)8{P(OPh)3}4: A 13C-{31P, 1H} NMR study

Variable temperature ¹³C-{³¹P, ¹H} NMR studies on Rh₄(CO)₈ {P(OPh)₃}₄ show that the solid state structure is maintained in solution at low temperature; at higher temperatures carbonyl migration occurs around the metal polyhedron with the lowest energy migration occurring via a Cotton type mechanism which also involves a rocking motion about the unique rhodium in the basal plane. At +82°C, the fast exchange limiting ¹³C-{³¹P, ¹H} and ³¹P spectra exhibit a quintet and doublet of quartets, respectively.     

17α-Konfigurierte 20-methylpregnan-derivate

A mixture of 1a+1b (17α), obtained by C-17-epimerization of pregnenolone (1a) was converted into 3a+3b by Wittig-reaction. 3a+3b were acetylated to a mixture of 4a+4b, from which 4b was isolated by cristallization of 3a and following AgNO₃-chromatography of the mother-liquors. Δ²⁰⁽²²⁾ → Δ¹⁷-doublebond-isomerization occurs by hydrogenation (Pd/C) of 3a (17β) to give 5. Hydrogenation (Pt-catalyst) of 4b (17α) leads to 8b, which was converted into the 20-methylpregnane-derivatives 7b, 9b–13b. By comparison with the 17β epimers 1a–4a, 7a–13a a spectroscopic determination of the relative configuration on C-17 of 17-alkylsubstituted steroids was possible.     

Use of13C/12C ratios for studying the origin of CO2 in sparkling wines

Summary ¹³C/¹²C ratios were measured in an attempt to determine the origin of the CO₂ in New Zealand commercial sparkling wines. This technique enabled a distinction to be made between CO₂ originating from C-3 plants, C-4 plants and that originating from an industrial source. With the additional measurement of the alcohol¹³C/¹²C ratios, it was possible to draw conclusions as to the wine making techniques used.

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Anwendung von¹³C/¹²C-Isotopenverhältnismessungen zur Bestimmung der CO₂-Herkunft in Handelssekt

Zusammenfassung Die Messung von¹³C/¹²C-Isotopenverhältnissen wurde dazu benutzt, um in neuseeländischem Handelssekt den Ursprung des CO₂ zu bestimmen. Mit dieser Methode konnte zwischen CO₂ aus C-3- und aus C-4-Pflanzenprodukten und CO₂ technischen Ursprungs unterschieden werden. Bei zusätzlichen¹³C/¹²C-Verhältnismessungen an Ethanol von Sektproben war es möglich, Rückschlüsse auf die Art der Sektherstellung zu ziehen.

     

Dynamic solvation effects on the endo/exo selectivity of the Diels-Alder reaction

The endo/exo stereoselectivity of the Diels-Alder cycloaddition between cyclopentadiene and 3-crotonoyl-2-oxazolidinone catalysed by Et₂AlCl is temperature- and solvent-dependent. Eyring plots of ln(endo/exo) versus 1/T show different inversion temperatures (T_inv) depending on the reaction solvent. Using toluene-d₈ we found a break temperature (T_NMR) in a variable temperature ¹³C NMR experiment of the starting oxazolidinone, and this T_NMR corresponded to the T_inv. In several cases the differential activation entropy manages the observed stereoselectivity.     

Configurationally and conformationally homogeneous cyclic n-aryl sulfimides—IV : Synthesis,configuration and stereochemistry of the rearrangement of 1,3-di-thiane-1-N-p-chlorophenylimides

1,3-Dithiane-1-N-p-chlorophenylimides (1,4-9) were prepared and their configuration and conformation was determined by ¹H and ¹³C NMR. The compounds were rearranged to the corresponding 2-(2'-amino-5'-chlorophenyl)-1, 3-dithianes (1U,4U,9U). The rearrangement reactions took place with ?95% stereospecifity. The mechanism of the reaction was investigated with the aid of analogs specifically deuterated at C-2.     

Kristall- und molekülstruktur zweier diastereomerer hexachlorothiolphosphorsäureester c6h9O4ps2cl6

By X-ray analysis the crystal and molecular structures of two diastereomeres of O,O-dimethyl-S-(2'-trichloro-1'-hydroxyethyl-1-mercapto-2-trichloroethyl) thiolphosphate have been established. The different chemical shifts of the signals of the methyl groups in the ¹HNMR-spectrum of one diastereomer, in contrast to the other, could be explained by the different effects of magnetic anisotropic groups of the methyl protons.     

New lignans from the heartwood of cleistanthus collinus

The isolation and characterisation of five new compounds and nine known compounds from the heartwood of Cleistanthus collinus are reported. The new compounds are wodeshiol 16,3,4-dihydrotaiwanin C 20, and three new glycosides 24, 25 and 26 of diphyllin and taiwanin E The ¹H and ¹³C NMR spectra of these compounds are also reported.     

Xylomexicanins E-H,new limonoids from Xylocarpus granatum

Four novel tetranortriterpenoids, xylomexicanins E–H (1–4), were isolated from the seeds of the Chinese mangrove, Xylocarpus granatum. Among them, xylomexicanin E (1) represents the first example of limonoid with azaspiro skeleton between B (pyrrolidine) and C rings, whose biosynthetic pathways were proposed. The structures were elucidated on the basis of one- and two-dimensional NMR (including ¹H, ¹³C NMR, DEPT, ¹H–¹H COSY, HSQC, HMBC, and NOESY) and confirmed by high-resolution mass spectrometry. Compound 2, the second example of a limonoid with a C-9–C-30 linkage, showed moderate activity against the A549 and RERF cell line with IC₅₀ value of 18.83 and 15.83 μM,     

The effect of polyether ligands on the solution structure of [Li]-α-(phenylthio)benzyllithium in tetrahydrofuran: A H,Li-HOESY NMR study

[⁶Li]-α-(phenylthio)benzyllithium 1-⁶Li was studied in THF/[D₈]THF solution (1:1) in the presence of several acyclic and cyclic polyether ligands by ¹H,⁶Li-HOESY, ¹H and ¹³C NMR spectroscopy. The question whether these ligands are bonded to lithium or not is important for physical–organic investigations as well as for studies of the ground state of (stereoselective) reactions of organolithium compounds in the presence of such ligands. Dimethoxyethane is not bonded to lithium under these conditions. The acyclic ethers diglyme and triglyme coordinate only weakly to the organolithium compound and form contact ion pairs (CIPs) at 25°C. At −80°C, CIPs are in equilibrium with separated ion pairs (SIPs). Very stable complexes of 1-⁶Li are obtained with crown ether ligands. Addition of 12-crown-4 and 15-crown-5, respectively, results in the exclusive formation of SIPs at 25°C and −80°C. With 18-crown-6, a CIP–SIP equilibrium is observed at 25°C which is shifted entirely to the SIP side at −80°C. Graphical analyses of the ¹H and ¹³C NMR spectra of the polyether complexes of 1-⁶Li revealed correlations between the chemical shifts of the para phenyl carbon C-5, the para phenyl proton H-5, the benzylic carbon C-1, and the proton–carbon coupling constant J(C-1,H-1) of 1-Li, which are useful probes for the charge distribution within the carbanionic moiety of 1-⁶Li in the respective complexes, and thus for the ion pair character as a function of the polyether complexation of lithium.     

The stereochemistry of 2,4-disubstituted γ-butyrolactones and 2,4,6-trisubstituted-5,6-dihydro-4H-1, 3-oxazines

2,4-Disubstituted butyrolactones and 2,4,6-trisubstituted-5,6 dihydro-4H-1,3-oxazines show similar features in their ¹H and ¹³C- NMR spectra. Two geminal ring hydrogens of cis isomers give rise to a complex ABXY spectra when the substituent is alkyl or aryl. In spectra of trans isomers these patterns are degenerated. When R is OMe(in 4) or OCOMe (in 6) the difference in chemical shifts of geminal protons and vicinal coupling constants cannot be used for diagnosis. In ¹³C spectra ring carbons C-2 and C-3 in lactones and C-4 and C-5 in oxazine of trans isomers show a small but consistent shift to higher fields.     

Three new monoterpene indole alkaloids from Psychotria umbellata Thonn.

Three new psychollatine-derived monoterpene indole alkaloids were obtained from Psychotria umbellata Thonn.: 3,4-Dehydro-18,19-β-epoxy-psychollatine (2), N⁴-[1-((R)-2-hydroxypropyl)]-psychollatine (3), and N⁴-[1-((S)-2-hydroxypropyl)]-psychollatine (4). Their structures were determined by ¹H and ¹³C NMR spectra, 2D correlations (COSY, HMQC, and HMBC), and mass and UV spectra. Compounds 3 and 4 were synthesized for structural confirmation and for the determination of the stereochemistry of the hydroxyl group.     

Chloroscabrolides, chlorinated norcembranoids from the Indonesian soft coral Sinularia sp.

Chemical analysis of the Indonesian soft coral Sinularia sp. (order Alcyonacea, family Alcyoniidae) afforded two known and three new C-4 norcembranoids, named chloroscabrolides A (3) and B (4) and prescabrolide (5). Chloroscabrolide A is a pentacyclic norcembranoid including an unprecedented THF-type ring to connect C-13 and C-15; furthermore, it is only the second chlorinated cembranoid derivative to be reported in the literature. The relative configuration of chloroscabrolide A has been established on the basis of a comparison between experimental ¹³C NMR data and DFT-calculated ¹³C NMR chemical shifts. All the isolated norcembranoids have been evaluated for iNOS protein inhibition.