The Structures and Syntheses of Rhizocarpic Acid and Epanorin<sup>1</sup>

Frank, Robert; Cohen, Solomon Solis; Coker, J. N.

doi:10.1021/ja01166a032

Cited by 11 publications

(14 citation statements)

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“…In 1950, Frank et al elucidated the structures of rhizocarpic acid (2) and epanorin (3) through degradation studies and confirmed the assignments through total synthesis (Scheme 1). 29 Ring-opening of pulvinic acid dilactone (5, PAD), a related natural product also (much later) isolated from lichens, 30 with the methyl esters of L-phenylalanine or L-leucine, gave rhizocarpic acid (2) and epanorin (3), respectively. The coidentities of the natural and synthetic products were confirmed by mixed melting points and comparison to the synthetic racemates, which had dramatically different melting points.…”

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confidence: 99%

“…The specific rotation of synthetic rhizocarpic acid also matched that reported for the natural product. 29 The same approach was later used to synthesize pulvinamide (1) (Scheme 1). 28 Surprisingly, NMR spectroscopic data for rhizocarpic acid (2) have never been published.…”

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confidence: 99%

“…■ RESULTS AND DISCUSSION Synthesis. The pulvinamides were synthesized by the route established by Frank, Clark, and Coker, 29,31 with some modifications. Commercial 2,5-diphenyl-1,4-benzoquinone (6) was brominated to give 7 in almost quantitative yield (Scheme 2).…”

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confidence: 99%

“…29 177−1778 °C]; [α] D 25 +115 (c 0.22, CHCl 3 ) [lit 29. [α] D 20 +110 (c 1.22, CHCl 3 )]; ECD (0.02 mg/mL, MeCN), λ max (Δε) 272 (68.0),…”

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confidence: 99%

“…Norrhizocarpic acid(9). Method B provided 9 as a yellow solid (86 mg, 94%): mp 88−90 °C [lit 29. 91−92 °C]; [α] D 25 +147 (c 0.42, CHCl 3 ) CHCl 3 )]; ECD (0.02 mg/mL, MeCN), λ max (Δε) 272 (65.9), 236 (−55.1), and 220 (71.7) nm; IR (ATR) ν max cm −1 3282 (N−H), 1756 (2 × C�O), 1663 (C�O); 1 H NMR (CDCl 3 , 600 MHz) δ 15.50 (br s, 1H, OH), 8.13 (dd, J = 8.5, 1.0 Hz, 2H, H-2‴/ 6‴), 7.46−7.37 (m, 5H, 5 × ArH), 7.32−7.28 (m [pseudo t], 1H, H-4‴), 7.26−7.20 (m, 3H, 3 × ArH), 7.15−7.11 (m [pseudo d], 2 × ArH), 6.91 (br d, J = 7.5 Hz, 2H, 2 × ArH), 6.26 (br d, J = 7.3 Hz, 1H, NH), 4.86 (ddd [app.…”

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confidence: 99%

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Synthesis, Characterization, and Bioactivity of the Lichen Pigments Pulvinamide, Rhizocarpic Acid, and Epanorin and Congeners

James

Vuong²,

Moggach

et al. 2023

J. Nat. Prod.

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The lichen natural products pulvinamide, rhizocarpic acid, and epanorin have been synthesized and characterized spectroscopically and by X-ray crystallography. The syntheses, by ring-opening of pulvinic acid dilactone (PAD), may well be biomimetic, given the well-known occurrence of PAD in lichen. The enantiomers, ent-rhizocarpic acid and ent-epanorin, and corresponding carboxylic acids, norrhizocarpic acid and norepanorin, were similarly prepared. All compounds were assessed for growth inhibitory activity against selected bacteria, fungi, a protist, a mammalian tumor cell line, and normal cells. Rhizocarpic acid is weakly antibacterial (Bacillus subtilis MIC = 50 μg/mL) and possesses modest but selective antitumor activity (NS-1 murine myeloma MIC = 3.1 μg/mL) with >10-fold potency relative to its enantiomer (MIC = 50 μg/mL).

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