Antiviral substances from plants

As a result of the intensive search for antiviral substances from medicinal plants, antiviral activity against HSV was found in extracts from Cedrela tubiflora Bertoni, leaves [79], from Prunella vulgaris L., a perennial plant commonly found in China, the British Isles and Europe [80] and from Trichilia glabra L. leaves [81]. Phytochemical studies indicate that these plants contain anionic PS as active constituents which may inhibit HSV by competing for cell receptors as well as by some unknown mechanisms after the virus has penetrated the cells. Furthermore, the in vitro antiviral activity demonstrated by extracts of the medicinal plant Achyrocline flaccida (Weinm.) D.C. on HSV-1 is exerted early during viral replication, essentially during viral adsorption to host... 

Attention is called to the pyrimidine antibiotics section in Part I of this review. Several of these natural products, including blasticidin, gougerotin, amicetin, bamicetin and plicacetin, are 1-substituted cytosines. Cytovirin is also a plant antiviral substance from Streptomyces olivochromogenus which yields cytosine on degradation [351]. 

Propolis is a resinous substance gathered by honeybees from various plants. It has been used as a traditional medicine since ancient times [9], as an anticarcinogenic [10], antifungal [11], antimicrobial [12], antiviral [13], and anti-inflammatory [14] agent. 

Our studies on biologically active substances of this plant led to isolation of diterpenoids showing cytotoxicity [8], inhibitory effects on fi-glucuronidase [9], H+,K+-ATPase [10-12], replication of herpes simplex virus type 1 (HSV-1) [8,13,14] and bone resorption stimulated by parathyroid hormone (PTH) [15], and antitumor [16] and antitumor promoting effects [17]. In addition, some flavonoids possessing cytotoxicity [18], inhibitory activity against [3-glucuronidase [19] and antiviral activity [20] were also obtained from whole plants. 

Propolis is a resinous substance collected by honeybees from leaf buds and cracks in the bark of various plants, mainly from poplar (Populus) species and, to a lesser extent, beech, horse chestnut, birch, and conifer. Bees mix the original propolis with beeswax and (5-glucosidase they secrete during the propolis collection. The resulting material is used by bees to seal holes in the hives, exclude drafts, protect against external invaders, and mummify their carcasses. Propolis has been used extensively in folk medicine for many years, and there is substantial evidence indicating that propolis has antiseptic, antifungal, antibacterial, antiviral, anti-inflammatory, and antioxidant properties [42]. 

---