**4. Kaempferol**

*Cucumber Economic Values and Its Cultivation and Breeding*

**2. Flavonoids**

**3.** *Cucumis sativus* **L***.*

These antidiabetic drugs are very effective in treating hyperglycemia, but despite this success, there has been increased side effects accompanying their use. Therefore, there is increased search for antidiabetic agents from medicinal plants with little or no adverse effects. Experimental reports have validated the presence of antidiabetic substances in medicinal plants [13–15]. One of such plants reported to have antidiabetic property is *Cucumis sativus*. Saidu *et al*.'s study reported the hypoglycemic property of methanolic fruit pulp extract of *Cucumis sativus* [16]. This chapter focuses on the antidiabetic principle identified in *Cucumis sativus* L.

Flavonoids are a class of plants secondary metabolites made up of polyphenolic structures that contribute to the color and fragrance of fruits and flowers, therefore, they constitute a significant part of the human diet [17]. As a large class, flavonoids are subdivided into groups based on the structure of their carbon rings and these include flavanols, flavones, chalcones, flavonones, flavanonols and isoflavones. They are abundantly distributed in vegetables, fruits and some beverages. Flavonoids possess a wide range of health-promoting properties like the antioxidant effect, anti-carcinogenic, anti-inflammatory and antidiabetic capabilities. They display these properties by modulating the functions of some cellular enzymes as well as inhibition of different enzymes like lipo-oxygenase, cyclo-oxygenase, phosphoinositide 3-kinase and xanthine oxidase [18, 19]. Therefore, they are indispensable components in various pharmaceutical, cosmetics and medicinal applications.

One of the flavonoids that possesses antidiabetic property is kaempferol.

*Cucumis sativus* L*.* also known as Cucumber is a creeping plant in the family Cucurbitaceae. It is a fruit native to India and widely cultivated around the world. It is consumed fresh in salads, fermented (pickles) and as cooked vegetable [20].

*High pressure liquid chromatographic profiling of the antidiabetic principle derived from Cucumis sativus* 

**14**

**Figure 1.**

*fruit juice.*

Kaempferol (3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-1-benzopyran-4-one also known as kaempferol-3, **Figure 2**) is a yellow crystalline flavonoid having a molecular weight of 286.23 with a melting point of 276–278 °C. It is soluble in hot ethanol and slightly soluble in water.

It has been isolated from different parts of different plants. Yang *et al*. separated kaempferol and its derivatives from the methanolic crude extract of *Neocheiropteris palmatopedata* by repeated column chromatography, using a Sephade*x* LH-20 column [30]. Orhan et al. reported the bioactivity-guided fractionation of *Calluna vulgaris* and isolated kaempferol galactoside using successive column chromatography techniques [31]. Ibitoye et al. also reported the bioactivity guided isolation of kaempferol from *Cucumis sativus* L. [26].

**Figure 2.** *Structure of Kaempferol.*

#### **5. Biosynthesis of kaempferol**

Kaempferol and its derivatives are synthesized in plants by different types of enzymes. Kaempferol is synthesized by condensation of 4-coumaroyl-CoA with tripropionyl-CoA to produce naringenin chalcone, this reaction is catalyzed by chalcone synthase [32]. Naringenin chalcone is then converted into a flavanone called naringenin, which is thereafter hydroxylated by flavanone 3-dioxygenase to produce dihydrokaempferol [33]. Finally, the introduction of a double bond at the C2-C3 position of dihydrokaempferol produces kaempferol.

There is no much data on the pharmacokinetics of Kaempferol, however, flavonoids are extensively metabolized by the colonic microflora [34, 35].

#### **Figure 3.** *Biological roles of Kaempferol.*

Intestinal permeability study of kaempferol shows it undergoes significant biotransformation, with only a small fraction of the unchanged kaempferol able to cross the intestinal barrier [36].

It has been isolated from tea as well as common vegetables and fruits like beans, broccoli, cabbage, grapes, strawberries, tomatoes, apples and grapefruit [37].

Kaempferol has anti-inflammatory and anti-cancer properties, protects the liver and prevent metabolic diseases (**Figure 3**). The most well-known of its properties are its anti-inflammatory effects by decreasing lipopolysaccharide (LPS)-induced tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1) expression and also by increasing the number of activated macrophages [38]. Kaempferol is a dietary flavonoids that occur in fruits, vegetables, beverages, chocolates, herbs and plants [39] and reported to possess anti-diabetic property.
