Jiří Slavík

1H and 13C NMR study of quaternary benzo[c]phenanthridine alkaloids

1H, 13C and in some cases also 15N chemical shifts of quaternary benzo[c]phenanthridine alkaloids (fagaronine, chelerythrine, chelilutine, chelirubine, nitidine, sanguilutine, sanguinarine, and sanguirubine) were systematically studied by NMR spectroscopy and ab initio calculations. The assignment of signals in the 1H and 13C NMR spectra was obtained from 2D NOE and gradient‐enhanced single‐quantum multiple bond correlation (GSQMBC) experiments. The ab initio geometry optimization using Gaussian 94 at the RHF/6–31 G** level, followed by the calculation of chemical shielding using the deMon/NMR code at the IGLO II level, were carried out in order to rationalize the assignment of individual experimentally determined resonances. Copyright

15N NMR study of isoquinoline alkaloids

15N NMR chemical shifts of 40 tertiary and quaternary isoquinoline alkaloids of six constitutional types are reported. The selected compounds belong to the classes of benzo[c]phenanthridine, protoberberine, benzylisoquinoline, aporphine, pavinane, and β‐carboline‐proaporphine alkaloids. The 15N chemical shifts were measured by gradient‐enhanced inverse‐detected single‐quantum (GSQMBC) and multiple‐quantum (GHMBC) multiple‐bond correlation experiments. The 1H–15N long‐range coupling constants determined from the phase‐sensitive GSQMBC spectra are also reported in order to facilitate optimization of multiple‐bond correlation experiments. Copyright

Some aspects of the chemistry of quaternary benzo[c]phenanthridine alkaloids

Abstract Quaternary benzo[ c ]phenanthridine alkaloids (QBA)are a relatively small class of natural products. These isoquinoline-derived alkaloids are conspicuous for their bright colours. They currently number 18, apart from evident artifacts and synthetic derivatives. QBA are widely distributed in a number of plant species of the Papaveraceae, Fumariaceae , and Rutaceae families. The most abundant sources of QBA are Sanguinaria canadensis, Chelidonium majus, Dicranostigma lactucoides, Macleaya cordata, M. microcarpa , and some Bocconia and Zanthoxylum species. Sanguinarine and chelerythrine, discovered in the 19th century, are the two best-known and commercially available QBA. Quaternary benzophenathridine cations display great susceptibility towards nucleophilic reagents. This nucleophilic attack is associated with a number of significant alterations in physical appearance, solubility, constitution, spectral properties, etc. A specific and very interesting chapter in the chemistry of the QBA concerns the formation of free bases. In analkaline environment, QBA are converted to bimolecular aminoacetal derivatives with an oxygen atom as the linking bridge. This review describes the distribution of QBA in plants. Methods of isolation and separation are included as well as biological activities. The main part of this chapter is devoted to the chemical reactivity of QBA, nucleophilic transformations and the formation of free bases.

SANGUINARINE PSEUDOBASE: RE-EXAMINATION OF NMR ASSIGNMENTS USING GRADIENT-ENHANCED SPECTROSCOPY

The formation of sanguinarine pseudobase (6‐hydroxydihydrosanguinarine) was studied by 1D and 2D NMR spectroscopy. The unequivocal evidence of a hemiaminal OH group and unambiguous 1H, 13C and 15N NMR assignments of this compound are discussed.

Determination of a symmetrical dimer structure in benzo[c]phenanthridine alkaloids by pulsed-field-gradient HMBC

Determination of a Symmetrical Dimer Structure in Benzo[c]phenanthridine Alkaloids by Pulsed-Field-Gradient HMBC

Structure elucidation of roemeridine by X-ray crystallography

Abstract The structure of roemeridine, the major alkaloid from Roemeria hybrida was established by X-ray crystallography. Structure-significant features of the 1H and 13C NMR spectral mass spectral fragmentations are reported.

Protopine hydro­chloride

Protopine hydrochloride (5,6,14,14a-tetrahydro-14a-hydroxy-7-methyl-8H-bis[1,3]benzodioxolo[5,6-a:4,5-g]quinolizinium chloride, C20H20NO5(+)-Cl(-)) is the salt of the isoquinoline alkaloid protopine. It is formed by the action of dilute hydrochloric acid on the protopine free base. The N-methyl and hydroxyl groups are in a trans configuration in the quinolizine ring and the central quinolizine N-C bond is unusually long [1.579 (2) A]. The crystal is a racemate.