Straightforward Synthesis of Highly Hydroxylated Phloroglucinol-Type 3-Deoxyanthocyanidins

Abstract

Phloroglucinol-type 3-deoxyanthocyanidins were synthesized through the interaction between phloroglucinol derivatives and arylethynylketones in acetic acid in the presence of aqueous hexafluorophosphoric acid. This methodology was applied to achieve the synthesis of natural apigeninidin, luteolinidin and ­tricetanidin with high yields.

Key words

acid-mediated condensation - heterocycles - ketones - phenols - 3-deoxyanthocyanidins

References and Notes

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16

Apigeninidin Trimethylether Hexafluorophosphate ( 10)
Purple powder; yield 93%; mp 201 °C. IR (KBr): 1652, 1640 (s, C=O), 1600, 1569, 1506, 1456, 1436, 1378, 1339, 1241, 1124, 1052, 834 (m, P-F) cm^-1. UV/Vis [MeOH-HCl (5%, 1 N)]: λ_max (ε) = 266 (24900), 394 (18000), 460 nm (13600 M^-1·cm^-1). ¹H NMR [300 MHz, CD₃CN-TFA-d ₁ (1%)]: δ = 3.96 (3 H, s, OCH₃), 4.07 (3 H, s, OCH₃), 4.09 (3 H, s, OCH₃), 6.80 (1 H, d, J = 2.2 Hz), 7.19 (2 H, m), 7.23 (1 H, dd, J = 2.2, 0.7 Hz), 8.05 (1 H, d, J = 8.5 Hz), 8.32 (2 H, m), 9.07 (1 H, dd, J = 8.5 Hz, ⁵ J = 0.7 Hz). ¹³C NMR [75 MHz, CD₃CN-TFA-d ₁ (1%)]: δ = 55.9/57.0/57.2 (OCH₃), 93.4, 99.8, 111.3, 113.4, 115.8, 120.8, 131.9, 148.7, 158.8, 159.0, 167.0, 171.4, 171.7. MS (ESI, positive mode): 297 (100) [M⁺]. HRMS (ESI): m/z calcd: 297.1121; found: 297.1109.

17

Chrysinidin Hexafluorophosphate ( 13)
Orange powder; yield 91%. IR (KBr): 3412 (s, br, OH), 1642 (s, C=O), 1580, 1563, 1541, 1381, 1340, 1269, 1239, 1203, 1193, 835 (m, P-F) cm^-1. UV/Vis [MeOH-HCl (5%, 1 N)]: λ_max (ε) = 274 (35400), 474 nm (36200 M^-1·cm^-1). ¹H NMR [300 MHz, CD₃CN-TFA-d ₁ (1%)]: δ = 6.81 (1 H, d, J = 2.2 Hz), 7.11 (1 H, dd, J = 2.2, 0.7 Hz), 7.72 (2 H, m), 7.84 (1 H, m), 8.13 (1 H, d, J = 8.4 Hz), 8.35 (2 H, m), 9.25 (1 H, dd, J = 8.4, 0.7 Hz). ¹³C NMR [75 MHz, CD₃CN-TFA-d ₁ (1%)]: δ = 95.7, 102.9, 111.2, 114.4, 128.9, 129.1, 130.0, 135.8, 150.5, 158.4, 159.4, 171.1, 171.4. MS (ESI, positive mode): 239 (100) [M⁺]. HRMS (ESI): m/z calcd: 239.0703; found: 239.0696.

18

All synthesized compounds exhibit NMR spectroscopic data identical to previously reported ones in the literature. [10-12]