Oligostilbenes groups

ABSTRACT More than 200 naturally occurring oligostilbenes isolated from plant kingdom are grouped into I-V structural types. They are a special kind of polyphenolic natural products with multi-faceted bioactivities. This article will review their classification, distribution, spectral characteristics, biological activities (anti-fungal, antibacterial, antioxidant, anti-inflammatory and anticarcinogenic activities, etc.) and mimetic biosynthesis. 

Most naturally occurring oligostilbenes belong to this type and are further divided into four groups (I-A, I-B, I-C and I-D) according to whether they contain oxa-cyclic rings and the type of polymerization. 

I-B group Oligostilbenes are polymerized directly from resveratrol monomers but do not contain any oxygen heterocyclic ring in their structures, such as ampelopsis D (21) [11]. Until now, 20 oligomers of this group have been found in plants. 

III- B group piceatanol oligostilbenes without any oxygen heterocyclic ring in their molecules. This type of polyphenol was formed directly from two units of 7 through carbon-carbon bond. Cassigarol A (45) is an example for this group. [30]. 

IV-B group oligostilbenes from 1 and 6 units connected by carbon-carbon bond forming cyclic or chain oligomers. For example, andalasin A (50) coupled with two units of 6 has been isolated from Morns macroua [34]. Gnetuhainin D (51) polymerized from 1 and 6 was obtained from Gnetum hainanense [35]. 

V. Oligostilbenes polymerized by other monostilbene units besides I-IV group. 

V-A group gnetuhainin K (52) is a polymer of 5 and 9 isolated from Gnetum hainanense [36]. Recently two oligostilbenes, gneafricanin A (53) and B (54) have been isolated from Gnetum africanum 53 was polymerized from 5 and 6 units, whereas 54 from 5 and 7 units [37]. 

Since the oligostilbenes have high molecular weights and mutiplet hydroxyl groups, it is generally difficult to obtain their molecular ion peaks in EI-MS except for some dimers or those without a hydroxyl group in the structures. Modern MS techniques, such as FAB-MS, FD-MS, ESI-MS and LSI-MS were used to obtain their molecular ion peaks. 

The IR spectra of oligostilbenes exhibit absorption bands for hydroxyl groups (3200 3500 cm 1), benzene group (1450-1600 cm 1) and double bonds (1610-1670 cm 1). There is a strong absorption band at 965 cm 1 if trans double bonds exist in the structure. An ambiguous absorption band at 730-675 cm 1 will appear in certain cases, if there are cis double bonds in the molecule. 

Two oligostilbenes of 44 and 123 (III-A group) from Cassia garrettiana were synthesized by Baba K. et al by 7 in acetone with Ag20 as oxidant [29] Fig. (9). 

The group of resveratrol oligomers comprises the largest number of oligostilbenes and is characterized by the polymerization of two to eight resveratrols. About 180 constituents of this group covering dimer to octamers have been reported, which is produced by diverse polymeric styles. 

Stilbenoids represent a group of important natural products in the plant kingdom. The developments of modem analytical methods accelerate the discovery of these compounds, and to this day more than 1,000 stilbenoids have been isolated. For the stilbenes, bibenzyls, and phenanthrenes, these three groups shared the feature of their nucleus with hydroxyls, methyl, methoxy, prenyl, geranyl, glycosyl, etc., substituents. The oligostilbenes and bisbibenzyls are formed by polymerization of stilbene and bibenzyl units, and the diverse polymerized patterns produced their... 

---