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Review
, 12 (4), 745-58

Litchi Flavonoids: Isolation, Identification and Biological Activity

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Review

Litchi Flavonoids: Isolation, Identification and Biological Activity

Jiangrong Li et al. Molecules.

Abstract

The current status of the isolation, identification, biological activity, utilization and development prospects of flavonoids found in litchi fruit pericarp (LFP) tissues is reviewed. LFP tissues account for approximately 15% by weight of the whole fresh fruit and are comprised of significant amount of flavonoids. The major flavonoids in ripe LFP include flavonols and anthocyanins. The major flavanols in the LFP are reported to be procyanidin B4, procyanidin B2 and epicatechin, while cyanindin-3-rutinside, cyanidin-3-glucoside, quercetin-3-rutinosde and quercetin-3-glucoside are identified as the important anthocyanins. Litchi flavanols and anthocyanins exhibit good potential antioxidant activity. The hydroxyl radical and superoxide anion scavenging activities of procyanidin B2 are greater than those of procyanidin B4 and epicatechin, while epicatechin has the highest alpha,alpha-diphenyl-beta-picrylhydrazyl radical (DPPH*) scavenging activity. In addition to the antioxidant activity, LFP extract displays a dose- and time-dependent inhibitory effect on human breast cancer, which could be attributed, in part, to its inhibition of proliferation and induction of apoptosis in cancer cells through upregulation and down-regulation of multiple genes. Furthermore, various anticancer activities are observed for epicatechin, procyanidin B2, procyanidin B4 and the ethyl acetate fraction of LFP tissue extracts. Procyanidin B4 and the ethyl acetate fraction show a stronger inhibitory effect on HELF than MCF-7 proliferation, while epicatechin and procyanidin B2 have lower cytotoxicities towards MCF-7 and HELF than paclitaxel. It is therefore suggested that flavonoids from LFP might be potentially useful components for functional foods and/or anti-breast cancer drugs.

Figures

Figure 1
Figure 1
Molecular structures of flavonoids adapted from Peterson and Dwyer (arrows indicate biosynthetic path) [3]. The basic structure consists of the fused A- and C-ring, with the phenyl B-ring attached to through its 1-position to the 2-position of the C-ring.
Figure 2
Figure 2
The flavylium cation. R1 and R2 are H, OH, or OCH3 while R3 is a glycosyl or H and R4 is OH or a glycosyl [3, 6].
Figure 3
Figure 3
Molecular formulae of epicatechin, procyanidin B2 and procyanidin B4.
Figure 4
Figure 4
pH-Dependent conformational rearrangement of anthocyanin molecule (G1: a sugar). At neutral pH anthocyans occur as chalcones with an open C ring (i). Under mildly acidic conditions the ring is closed to form a carbinol pseudobase (ii). In strong acid (pH 2), ring C acquires aromaticity involving a flavylium cation, which imparts intense colour to the molecule (iii). In alkali, oxidation of ring A generates a quinoid structure with elimination of the positive charge, this species is also coloured (iv). The ring-opened chalcone can be reformed at neutral pH [13].
Figure 5
Figure 5
Proposed mechanism for cyanidin–DNA interation which leads to the formation of cyanidin–DNA copigmentation complex [6,51].

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