**2.4 Antimicrobial activity**

Antimicrobial activity of oleuropein, tyrosol and hydroxytyrosol has been studied *in vitro* against bacteria, viruses and protozoa (Bisignano et al., 1999).

The *in vitro* antimycoplasmal activity of HT has been investigated, concluding that this compound might be considered as an antimicrobial agent for treating human infections caused by bacterial strains or casual agents of intestinal or respiratory tract (Furneri et al., 2004).

It has been shown that polyphenols from olive oil are powerful anti-*Helicobacter Pylori* compounds *in vitro* (Romero et al., 2007), a bacteria linked to a majority of peptic ulcers and to some types of gastric cancer.

### **2.5 Antiinflammatory activity**

Inflammation and its consequences play a crucial role in the development of atherosclerosis and cardiovascular diseases. Polyphenols have been shown to decrease the production of inflammatory markers, such as leukotriene B4, in several systems (Biesalski, 2007).

The effect of hydroxytyrosol on platelet function has been tested. Hydroxytyrosol was proven to inhibit the chemically induced aggregation, the accumulation of the proaggregant agent thromboxane in human serum, the production of the pro-inflammatory molecules leukotrienes and the activity of arachidonate lipoxygenase (Visioli et al., 2002).

Recently, it has been described that HT-20, an olive oil extract containing about 20% of hydroxytyrosol, inhibits inflammatory swelling and hyperalgesia, and suppresses proinflammatory cytokine in a rat inflammation model (Gong et al., 2009).

### **2.6 Antiviral activity**

Hydroxytyrosol and oleuropein have been identified as a unique class of HIV-1 inhibitors that prevent HIV from entering into the host cell and binding the catalytic site of the HIV-1

Biological Properties of Hydroxytyrosol and Its Derivatives 379

As an example, benzyl groups have been used to carry out the HT esterification under basic conditions, followed by catalytic hydrogenation to remove the protective groups (Gordon et

Scheme 2. Synthesis of hydroxytyrosyl acetate via benzylation of phenolic hydroxyls

synthesis of HT upon reduction with LiAlH4 and acidic deprotection.

O

MeO H O OMe

MeO

O

O

HO OH

HO

Scheme 3. Synthesis of hydroxytyrosyl acetate via methyl orthoformate-protected

HO OH

LiAlH4

Amberlyst 15 MeOH

O

LiAlH4

HO

+ MeO

O

HO

H

H

MeO O OH

MeO O O

HO O

AcCl Py, THF

O OH

O

Amberlyst 15 K2HPO4, KH2PO4 MeOH

O

A two-step procedure involving the reaction of methyl orthoformate-protected hydroxytyrosol with acetyl chloride, and hydrolytic deprotection in phosphate buffer under very mild conditions (pH=7.2) to get hydroxytyrosyl acetate (87% overall yield) (Scheme 3) was also described as a successful procedure for the preparation of HT-derived esters (Gambacorta et al., 2007). The key synthetic orthoester intermediate was also used for the

**3.1.1.1 Protection of phenolic hydroxyl groups** 

al., 2001), as depicted in Scheme 2.

HO

HO OMe

hydroxytyrosol.

O

HC(OMe)3 Amberlyst 15

benzene

integrase. Thus, these agents provide an advantage over other antiviral therapies in which both, viral entry and integration, are inhibited (Lee-Huang et al., 2007a, 2007b, 2009).

HT and its derivatives are also useful, when applied topically, as microbicide for preventing HIV-infection, as well as other sexually transmitted diseases caused by fungi, bacteria or viruses (Gómez-Acebo et al., 2011). Furthermore, it has been reported that hydroxytyrosol inactivated influenza A viruses, suggesting that the mechanism of the antiviral effect of HT might require the presence of a viral envelope (Yamada et al., 2009).
