Tetrahydroisoquinoline alkaloids of the Mexican columnar cactus Pachycereus Weberi

Eight tetrahydroisoquinoline alkaloids have been crystallized and identified from the nonphenolic and phenolic extracts of the giant Mexican cereoid cactus, Pachycereus weberi (Coult.) Br. and R. The identities were established as 5,6,7-trimethoxy-1,2,3,4- tetrahydroisoquinoline (nortehuanine) 1; 7,8-dimethoxy-1,2,3,4-tetrahydroisoquinoline (lemaireocercine) 2; 7-methoxy-1, 2,3,4-tetrahydroisoquinoline (weberidine) 3; 5,6,7,8-tetramethoxy-1,2,3,4-tetrahydroisoquinoline (weberine) 4; 6,7- dimethoxy-1,2,3,4-tetrahydroisoquinoline (heliamine) 5; 2-methyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (N- methylheliamine or oxymethyl-corypalline) 6; 2-methyl-5,6,7-trimethoxy-1,2,3,4-tetrahydroisoquinoline (tehuanine) 7; and 1,2-dimethyl-6,7-dimethoxy-8-hydroxy-1,2,3,4-tetrahydroisoquinoline (pellotine) 8. Compounds 1- 4 have not been identified previously as natural compounds, while compounds 5-8 are previously known cactus alkaloids.     

13C NMR spectral analysis of some isoquinoline alkaloids

The ¹³C NMR spectra of some isoquinoline and tetrahydroisoquinoline alkaloids and their corresponding N-methosalts and of the bisbenzylisoquinoline alkaloid isochondodendrine were recorded and the signals assigned. The substituent shielding effects and the ¹³C¹H long range couplings were analysed and utilized in the spectral interpretation.     

Two simple tetrahydroisoquinoline alkaloid N-oxides from cacti

Tehuanine N-oxide was isolated from Pachycereus pringlei, and deglucopterocereine N-oxide was isolated from Pterocereus gaumeri. These     

Structural confirmation of dihydrocinnamic acids from Adiscanthus fusciflorus by 13C NMR

In the wood of Adiscanthus fusciflorus six known alkaloids 4-methoxy-2-quinolone, 1-methyl-4-methoxy-2-quinolone, dictamine, skimmianine, γ-fagarine and N-methylflindersine and two new dihydrocinnamic acids 3-[2′,6′-dimethoxy-6″,6″-dimethylpyrano(2″,3″:4′, 3′)phenyl]-propionic acid and its methyl ester were identified. The structures of the dihydrocinnamic acid derivatives were confirmed by ¹³C NMR.     

13 C NMR Chemical shifts and carbon-proton coupling constants of some furocoumarins and furochromones

The ¹³C NMR spectra of a variety of furocoumarins, dihydrofurocoumarins and furochromones are reported. The signals were assigned using carbon-proton coupling constants, ring annullation shifts, nuclear Overhauser effect considerations and shift effects caused by monothioester formation. Substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. Methoxyl induced shifts of 5- and 8-substituted furocoumarins are additive, but their effects cannot be transferred to the furochromone system.     

13C NMR Spectra of some D:A-friedo-oleananes

The ¹³C NMR signals of D:A-friedo-olean-7-one, putranjivadione, D:A-friedo-olean-22-one, D:A-friedo-olean-3,22-dione, and Salacia triterpene R have been assigned using off-resonance decoupling and lanthanide induced shift techniques. ¹³C NMR data provide further evidence for the boat-boat conformation for the D and E rings of D:A-friedo-oleananes in solution.     

The 13C NMR spectra of some rosane diterpenoids

The ¹³C NMR signals of rosenonolactone have been assigned utilizing the ¹³C-¹³C couplings in material obtained biosynthetically from sodium [1,2-¹³C₂] acetate.     

Carbon-13 NMR analysis of cyclic peptide alkaloids

The chemical shifts of the carbons of the peptide alkaloids discarine-A, discarine-B, lasiodine-A, lasiodine-B, pandamine, pandaminine and hymenocardine have been assigned.     

Constituents of Papaver bracteatum: O-methyl-α-thebaol and 10-n-nonacosanol. Lanthanide-induced chemical shifts in 1H NMR and 13C NMR

Two non-alkaloidal constituents were identified in Papaver bracteatum: O-methyl-α-thebaol and 10-n-nonacosanol. O-Methyl-α-thebaol is a new natural compound. The presence of isothebaine is confirmed. Lanthanide-induced chemical shifts can be used for the assignments of the ₁₃C NMR chemical shifts of isothebaine and phenanthrenes. The use of lanthanide-induced chemical shifts in the identification of methoxyl resonances in ₁H NMR is discussed.     

The 13C NMR spectra of some ent-18-hydroxykaur-16-enes

The ¹³C NMR spectra are reported for thirteen ent-18-hydroxykaur-16-enes and their value for determining the C-4 stereochemistry is discussed.     

13C NMR studies of some naturally occurring amentoflavone and hinokiflavone biflavonoids

The ¹³C NMR spectra of a range of amentoflavone and hinokiflavone biflavonoids are reported, most for the first time. Substituent shifts relating to the interflavonoid linkages and to specific methylation patterns are defined and appear to be of diagnostic value.     

13C NMR spectra of some naturally occurring binaphthoquinones and related compounds

¹³C NMR chemical shift assignments have been shown to be diagnostic for the establishment of the dimeric linkage of some naturally occurring binaphthoquinones. The unsymmetric ¹³C and ¹H spin-spin coupled pattern observed in the ¹H coupled ¹³C NMR spectrum of plumbagin for C-6 has also been noticed earlier with the related compound juglone. The nature of these effects has been substantiated for the first time using benzene induced solvent shifts and D₂O exchange. ¹³C chemical shift assignments of plumbagin reported earlier for C-6 and C-8 have been revised.     

13C NMR spectroscopy of neolignans

The ¹³C NMR spectra of 15 neolignans of several structural types and two lignans were analyzed and their carbon shifts assigned. The shifts of pyrogallol ether and ethyl phenyl carbinyl ether models were used in this connection. The stereochemistry of a dimeric sideproduct in the preparation of the latter models was determined by ¹³C NMR analysis.     

13C NMR spectral analysis of eperuane diterpenes

The ¹³C NMR spectra of some eperuane diterpenes have been recorded and the signals assigned. The substituent shielding effects in these compounds, in comparison with those observed in other series of diterpenes, are also presented.     

Solid-state 13C NMR spectroscopy of a 13C carbonyl-labeled polypeptide

High resolution structural elucidation of macromolecular structure by solid-state nuclear magnetic resonance requires the preparation of uniformly aligned samples that are isotopically labeled. In addition, to use the chemical shift interaction as a high resolution constraint requires an in situ tensor characterization for each site of interest. For ¹³C in the peptide backbone, this characterization is complicated by the presence of dipolar coupled ¹⁴N from the peptide bond. Here the ¹³C₁-Gly₂ site in gramicidin A is studied both as a dry powder and in a fully hydrated lipid bilayer environment. Linewidths reported for the oriented samples are a factor of five narrower than those reported elsewhere, and previous misinterpretations of the linewidths are corrected. The observed frequency from oriented samples is shown to be consistent with the recently determined structure for this site in the gramicidin backbone. It is also shown that, whereas a dipolar coupling between ¹³C and ¹⁴N is apparent in dry preparations of the polypeptide, in a hydrated bilayer the dipolar coupling is absent, presumably due to a `self-decoupling' mechanism.