In 2004, a new anti-HIV alkaloid named drymaritin was isolated from Drymaria diandra. The authors identified the alkaloid as 5-methoxycanthin-4-one on the basis of spectroscopic data. Here we describe a synthetic approach that unambiguously gave 5-methoxycanthin-4-one, but the synthetic product showed spectroscopic data significantly different from those of the Drymaria alkaloid. Extensive re-evaluation of the spectroscopic data published for this and related alkaloids has led to the conclusion that drymaritin does not have a canthin-4-one backbone, but is identical to the known alkaloid cordatanine (4-methoxycanthin-6-one).
Key steps in the new approach to enantiopure title compounds (IV) are a kinetic enzymatic resolution of racemic alcohol (I) and the Grubbs I catalyzed stereoselective ring‐closing metathesis to the desired (Z)‐lactones.
3-Substituted isocoumarins were prepared in a short and efficient way from 2-iodobenzoic acid and terminal alkynes in a one-pot Sonogashira reaction. Catalytic hydrogenation gave the corresponding dihydroisocoumarins. The cytotoxic activities of the resulting compounds against human leukaemia cell line (HL 60) were determined in a MTT assay, and structure-activity relationships are discussed.
An analogon of the alkylpyridine alkaloid ikimine A (1) was prepared in six steps starting from undec-10-ynoic acid. A key step in this synthesis was a Sonogashira coupling of the alkyne and 3-iodopyridine, followed by hydrogenation of the alkyne, reduction of the ester to the primary alcohol and oxidation to the corresponding aldehyde. This aldehyde was converted to the ikimine A analogon with O-methyl hydroxylamine hydrochloride. This product and the intermediate alkylpyridines were tested in the agar diffusion assay for antibacterial and antifungal activities.
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