Many new natural product-derived pharmaceutically active compounds and compositions, each effective in treating an array of diseases and maladies including various tumors and HIV, have been reportedly isolated from different sources of vegetation, including the bark of yew trees, needles, leaves, fungi, and cell culture of many different species; vegetables such as West African yams; and Chinese and Indian herbs. Other sources include vegetation from South American rainforests. Many of the sources of such natural products are historical in nature and/or are known from folklore. Recent studies have provided potentially new biodiverse pharmaceutical compounds such as paclitaxel, which is obtainable from several species, including various portions of T. brevifolia, the Western yew tree, and other yew species such as T. baccata, T. cuspidata, T. wallichiana, T. media, T. canadensis, T. chinensis and T. yunnanensis as well as from T. wardii, T. capitata, T. brownii, T. gem, T. globosa, T. floridana, T. hicksii, T. densiformis, and T. darkgreen spreader, in addition to cultured plant cells and fungi. The novel compounds and their semisynthetic brominated and chlorinated analogs prepared from T. yunnanensis extract show strong activity against several types of tumors.