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This phytochemical study presents the isolation of eight alkaloids from Zephyranthes citrina Baker. The structures of the new alkaloids, zephycitrine ( 1 ) and 6-oxonarcissidine ( 2 ), were established by analysis of spectroscopic and spectrometric data. Processing the EtOH extract under acid-base conditions yielded the unreported isolation artifacts 3 and 4 . This work also provides analytical data for alkaloids not properly described in the literature ( 5 and 6 ). The hippeastidine/zephyranine scaffolds in derivatives 3 , 4 , and 8 - 10 are also thoroughly discussed. Furthermore, a cytotoxicity screening of 25 Amaryllidaceae alkaloids isolated from Z. citrina was performed. Only the known alkaloids haemanthamine ( 12 ), haemanthidine ( 13 ), and lycorine ( 27 ) showed significant cell growth inhibition.

The incidence rate of malaria and the ensuing mortality prompts the development of novel antimalarial drugs. In this work, the activity of twenty-eight Amaryllidaceae alkaloids (1–28) belonging to seven different structural types was assessed, as well as twenty semisynthetic derivatives of the β-crinane alkaloid ambelline (28a–28t) and eleven derivatives of the α-crinane alkaloid haemanthamine (29a–29k) against the hepatic stage of Plasmodium infection. Six of these derivatives (28h, 28m, 28n and 28r–28t) were newly synthesized and structurally identified. The most active compounds, 11-O-(3,5-dimethoxybenzoyl)ambelline (28m) and 11-O-(3,4,5-trimethoxybenzoyl)ambelline (28n), displayed IC50 values in the nanomolar range of 48 and 47 nM, respectively. Strikingly, the derivatives of haemanthamine (29) with analogous substituents did not display any significant activity, even though their structures are quite similar. Interestingly, all active derivatives were strictly selective against the hepatic stage of infection, as they did not demonstrate any activity against the blood stage of Plasmodium infection. As the hepatic stage is a bottleneck of the plasmodial infection, liver-selective compounds can be considered crucial for further development of the malaria prophylactics. [ABSTRACT FROM AUTHOR]

Clivia miniata (Amaryllidaceae) is an herbaceous evergreen flowering plant that is endemic to South Africa and Swaziland and belongs to one of the top-10 traded medicinal plants in informal medicine markets in South Africa. The species has been reported as the most important component of a traditional healer's pallet of healing plants. Eighteen known Amaryllidaceae alkaloids (AAs) of various structural types, and one undescribed alkaloid of homolycorine-type, named clivimine B (3), were isolated from Clivia miniata. The chemical structures of the isolated alkaloids were elucidated by a combination of MS, HRMS, 1D and 2D NMR techniques and by comparison with literature data. Compounds isolated in a sufficient quantity, and not tested previously, were evaluated for their in vitro acetylcholinesterase (AChE; E.C. 3.1.1.7) and butyrylcholinesterase (BuChE; E.C. 3.1.1.8) inhibition activities. [ABSTRACT FROM AUTHOR]

Narciindole A, the first representative of Amaryllidaceae alkaloids with an indol-3-ylmethanone framework, was isolated from bulbs of Narcissus pseudonarcissus (L.) cv. Carlton, together with carltonine D and carltonine E, which share the same unusual structural motif as dimeric carltonine C (reported in 2020), exhibiting atropisomerism. Unambiguous structure elucidations have been achieved by NMR spectroscopy, HRMS, and comparison with literature data of related alkaloids. Furthermore, the chirality of known alkaloids with a galanthindole biaryl core was revised using optical rotation. Last, but not least, a biosynthetic pathway for dimeric carltonine-type alkaloids was proposed. Unfortunately, in terms of biological activity, the isolated alkaloids showed only moderate inhibition of human acetylcholinesterase and/or butyrylcholinesterase. Unreported Amaryllidaceae alkaloids and their 1H NMR spectra, where 2 and 3 show doubling of signals caused by an omitted type of chirality – atropisomerism. [Display omitted] • Narciindole A, the first alkaloid with an indolyl carbonylphenylhexahydroindole core. • Two alkaloids extended a rare carltonine-type of Amaryllidaceae alkaloids. • Omitted axial chirality straightened up. • Reductive amination, the final steps of carltonines biosynthesis. • Significant selective inhibition of h BuChE reported for carltonines. [ABSTRACT FROM AUTHOR]