Isolation and synthesis of pygmanilines, phenylurea derivatives from the Northeastern Atlantic lichen Lichina pygmaea

Mahajan, Nipun; Chadda, Rekha; Calabro, Kevin; Solanki, Hiren; Connell, Enda O'; Murphy, Paul V.; Thomas, Olivier P.

doi:10.1016/j.tetlet.2017.02.037

Cited by 8 publications

(2 citation statements)

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“…Ureas 1529, 1530 and biaryls 1531-1533, the latter three reported as NPs for the rst time, were isolated from the lichen Lichina pygmaea. 733 Moderate antioxidant activities were observed for 1529, 1530 and 1533 and the structures of 1529 and 1530 were conrmed by synthesis. A new avone O-glycoside sulfate, thalassiolin D 1534 was isolated from extracts of the seagrass Thalassia hemprichii.…”

Section: Miscellaneousmentioning

confidence: 98%

Marine natural products

et al. 2019

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Section: Miscellaneousmentioning

confidence: 98%

Marine natural products

et al. 2019

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“…Macaurea A 17 was accessed in 96% yield from the Boc proline and CDI derived compound 16 via an initial Boc group deprotection using HCl (10.0 equiv) in dioxane and dichloromethane followed by reaction with 8m and triethylamine (1.0 equiv) (Scheme a). An analogous approach was applied to the synthesis of the unsymmetric urea pygmaniline A 18 , a natural product extracted from the lichen Lichina pygmaea that shows antioxidant properties . Treatment of in situ generated carbamoylimidazole 8o at 40 °C with 1.3 equiv of 2,4-dimethoxyaniline and triethylamine (1.5 equiv) afforded pygmaniline A 18 in 79% yield following flash column chromatography (Scheme b).…”

Section: Resultsmentioning

confidence: 99%

N-Alkyl Carbamoylimidazoles as Isocyanate Equivalents: Exploration of the Reaction Scope for the Synthesis of Ureas, Hydantoins, Carbamates, Thiocarbamates, and Oxazolidinones

et al. 2022

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The reaction of the HCl or trifluoroacetic acid salts of primary amines with carbonyldiimidazole (CDI) is shown to be a preparatively useful method for forming monosubstituted carbamoylimidazoles (28 examples) without the formation of symmetrical urea side products. The utility of these air-and water-stable crystalline carbamoylimidazole reagents was demonstrated by their reactions as blocked or masked isocyanate equivalents. Reaction with various classes of nucleophiles provides access to useful functional groups including ureas, carbamates, thiocarbamates, hydantoins, and oxazolidinones. A parallel synthesis library of 30 ureas was generated by the reaction of 6× carbamoylimidazole intermediates with 5× amines and triethylamine. The unsymmetrical urea-containing natural products macaurea A and pygmaniline A were also prepared in good yields (95% over four steps and 79% over three steps, respectively) using this approach. The reaction of carbamoylimidazoles with amino acid methyl esters followed by microwave irradiation in aqueous media gives hydantoins in high yields, further demonstrating the ability of carbamoylimidazoles as isocyanate surrogates. Three hydantoin-containing natural products including macahydantoin D and meyeniihydantoin A were prepared in nearly quantitative yields from proline methyl ester and carbamoylimidazoles. The reaction of carbamoylimidazoles with alcohols and thiols under basic conditions affords carbamates and thiocarbamates, respectively, in good yields. Lastly, a method for the preparation of chiral oxazolidinone heterocycles from chiral epoxy alcohols is demonstrated using a double displacement approach. The reactions occur with high regio-and stereoselectivity (dr ≥ 15:1 by 1 H NMR) via a domino attack of the corresponding alkoxides with carbamoylimidazoles followed by an intramolecular attack of the in situ generated urea anion at the proximal position of the epoxide group.

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