Nonenzymatic exogenous and endogenous antioxidants play an important role in human health and act as preservatives for cosmetics, pharmaceuticals, and food products. This chapter will discuss the chemical structure and mechanism of action of the most important nonenzymatic small exogenous and endogenous organic molecules that act as antioxidants. The chapter will focus on the structural features, functional groups, properties, biosynthetic origin, and mechanism of action of such antioxidants. It also covers damages that free radicals create and the mechanisms by which they are neutralized by the various antioxidants. The scope of this chapter will be limited to nonenzymatic exogenous and endogenous antioxidants since enzymatic antioxidants have been discussed extensively in several reviews.

Natural products are regarded as vital key source of lead compounds for drug discovery due to their structural diversity and broad array of biological activities. Phenylpropanoid sucrose esters are naturally occurring compounds isolated from various plants and are structurally characterized by a sucrose core connected to one or more Ph-CH=CH-CO- moieties through an ester linkage. These compounds were extensively used in folk medicine and are found to possess many biological activities such as antitumor, antibacterial, antioxidant, antiviral, anti-inflammatory, neuro-protective and glycosidase inhibitory activities. This extensive review, which is the first of its kind on phenylpropanoid sucrose esters, aims to provide an up-to-date account of naturally occurring known phenylpropanoid sucrose esters with special focus on their sources, structures, biological and pharmacological activities.