C8-selective biomimetic transformation of 5,7-dihydroxylated flavonoids by an acid-catalysed phenolic Mannich reaction: Synthesis of flavonoid alkaloids with quercetin and (–)-epicatechin skeletons

Flavoalkaloids with a Pyrrolidinone Ring from Chinese Ancient Cultivated Tea Xi-Gui

“…The strong ROESY correlation of the signal at the A-ring (δ H 6.03, H-8) with 7-OH proton (δ H 9.45) and the signals (δ H 2.76, 3.02, H-4α, 4β) with 5-OH proton (δ H 8.55) (Figure S19) both revealed the attachment of the N -ethyl-2-pyrrolidinone group at the C-6 position, indicating that the proton signal (δ H 6.03) belongs to H-8 (Table ). Besides the similar key HMBC correlations to those of compound 1 , correlations between 5-OH (δ H 8.55) and C-5, 6, and 10 (δ C at 154.9, 107.1, 98.8, respectively) were also observed in the HMBC spectrum of compound 2 (Figure ). …”

Novel Flavoalkaloids from White Tea with Inhibitory Activity against the Formation of Advanced Glycation End Products

“…These 1 H− 1 H COSY and HMBC correlations revealed the presence of a Nethyl-2-pyrrolidinone ring (Figure 4). The weak ROESY correlations of a signal at the A ring (δ H 6.07, CH-8) with that of the B ring (δ H 6.51, CH-2′, CH-6′), C ring (δ H 5.00, CH-2), and 7-OH proton (δ H 9.44) (Figure S12 of the Supporting Information) allowed the attachment of the Nethyl-2-pyrrolidinone group at the C-6 position, and the proton signal (δ H 6.07) belongs to the C-8 position (Figure 4), 34 which are proven with the corresponding HMBCs from H-5′′′ (δ H 5.43) to C-5 (δ C 156.4) and C-7 (δ C 158.5).…”

Novel Cinnamoylated Flavoalkaloids Identified in Tea with Acetylcholinesterase Inhibition Effect

“…These HMBC and 1 H− 1 H COSY signals confirmed that an N-ethyl-2-pyrrolidinone ring is present in the structure (Figure 2). The substitution of this N-ethyl-2-pyrrolidinone moiety at the C-6 position can be deduced by the weak ROESY correlations (δ H 6.07, CH-8)/(δ H 6.68, 6.64 CH-2′, CH-6′), C ring (δ H 5.02, CH-2), and 7-OH proton (δ H 9.23) (Figure 2), 32 which is further proved from the corresponding HMBC data correlation, H-5‴ (δ H 5.12) to C-5 (δ C 155.2) and C-7 (δ C 155.2).…”