Abstract
Galanthamine, an acetylcholinesterase inhibitor marketed as a hydrobromide salt (Razadyne®, Reminyl®) for the treatment of Alzheimer’s disease (AD), is obtained from Amaryllidaceae plants, especially those belonging to the genera Leucojum, Narcissus, Lycoris and Ungernia. The growing demand for galanthamine has prompted searches for new sources of this compound, as well as other bioactive alkaloids for the treatment of AD. In this paper we report the isolation of the new alkaloid 11β-hydroxygalanthamine, an epimer of the previously isolated alkaloid habranthine, which was identified using NMR techniques. It has been shown that 11β-hydroxygalanthamine has an important in vitro acetylcholinesterase inhibitory activity. Additionally, Hippeastrum papilio yielded substantial quantities of galanthamine.
Highlights
The object of many studies, Amaryllidaceae alkaloids contain a wide range of chemical structures and interesting biological properties [1], showing pronounced antimalarial [2], antitumoral [3] and acetylcholinesterase inhibitory activity [4]
Using modern 2D NMR, we report the correct assignment of 11β-hydroxygalanthamine, a new alkaloid from Hippeastrum papilio, confirming that the previously reported habranthine is 11αhydroxygalanthamine
Fresh leaves were submitted to alkaloid extraction. Their alkaloid profile obtained by TLC and GC-MS was quite similar to that observed for bulbs, with additional traces of narwedine (3) and vittatine (7), which were identified by comparing their GC-EI-MS spectra and Kovats retention indices (RI) with our own library database
Summary
The object of many studies, Amaryllidaceae alkaloids contain a wide range of chemical structures and interesting biological properties [1], showing pronounced antimalarial [2], antitumoral [3] and acetylcholinesterase inhibitory activity [4]. Plants of the genus Hippeastrum, which is endemic to South America, have yielded interesting bioactive compounds such as montanine, with significant psychopharmacological and acetylcholinesterase inhibitory activity [7,8] and candimine, active against Trychomonas vaginalis [9]. We have identified six known alkaloids, including significant quantities of galanthamine which was the main alkaloid isolated, from the bulbs and leaves of Hippeastrum papilio (Ravenna) Van. Scheepen, which grows in Southern Brazil. We have clarified the correct position of the hydroxyl-substituent in the alkaloid habranthine through the isolation of its epimer, the new alkaloid. Habranthine was isolated from Pancratium maritimum without certainty about the stereochemistry of the hydroxyl substituent at position 11 in the galanthamine-type skeleton. Using modern 2D NMR, we report the correct assignment of 11β-hydroxygalanthamine, a new alkaloid from Hippeastrum papilio, confirming that the previously reported habranthine is 11αhydroxygalanthamine. 11β-hydroxygalathamine has demonstrated a good ability to inhibit the acetylcholinesterase enzyme, with IC50 of 14.5 ± 0.33 μM
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