Mixtures and Other Compounds

Ayurvedic medicine, Chinese traditional medicine, and many other ethnomedicinal systems rely on both "pure" single-plant preparations and mixed formulations with many plants. Propolis, a crude extract of the balsam of various trees, contains terpenoids, flavonoids, benzoic acids and esters, phenolic acids and esters, and was found to inhibit hemagglutination activity of influenza virus, acyclovir-resistant HSV-1, adenovirus 2, VSV, and poliovirus, because the compounds in the mixture act synergistically, while flavone and flavonol were active in isolation against HSV-1 [119]. On the other hand, the kaempferol crassirhizomoside and sutchuenoside of Dryopteris crassirhizoma inhibited reverse transcriptase-associated DNA polyme-

rase and RNase H activities [120]. Similarly the flavonoids, triterpenoids, and their glycosides isolated from Azadirachta indica leaf inhibited plaque formation in six antigenic types of Coxsackie virus B by interfering with the early steps of replication [121], while Artemisia capillaris inhibited HIV replication due to a mixture of three compounds [122].

Reports on the antiviral activity of other phytochemicals are very scarce. The methyl esters dehydrochebulic acid and methyl brevifolin carboxylate isolated from Phyllanthus urinaria have anti-HBV activity [123], while diprenylated bibenzyl of Glycyrrhiza lepidota leaf extract inhibited HIV-1 (Table 15.1) replication [124]. An extract of fresh garlic, called ajoene, can protect CD4 cells from HIV attack early in the viral life cycle and its anti-HIV activity is 45 times more powerful than that of dextran sulfate. This is because the garlic impairs the activities of liver enzymes that process protease inhibitors and thereby raises the protease inhibitor levels [16]. The free hydroxyl group of galloyl residues of tertagalloyl-glucopyranose obtained from Juglans mandshurica inhibited reverse transcriptase and RNase H activity; while asiaticoside of Centella asiatica and mangiferin of Mangifera indica, used as a herpesvirus remedy in Thailand, have anti-HSV activities. Interestingly, combinations of any of these extracts with acyclovir resulted in additive or synergistic inhibition of HSV-2 [125].

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