Metabolites 2012.2 308 Undoubtedly one of the most famous natural product discoveries derived from a fungus (microorganism)is that of penicillin (7)from the fungus,Penicillim nom discovered by Fleming in 1929 [33].A countercurrent extractive separation technique which produced 7 in high yields was required for experimentation that ultimately saved countless lives and won Chain and Florey (together with Fleming)the 1945 Nobel prize in Physiology and Medicine (Figure 2)[34].This discovery led to the re-isolation and clinical studies by Chain,Florey and co-workers in the early 1940s and commercialization of synthetic penicillins,which ultimately revolutionized drug discovery research [35-38]. After publication of the first clinical data on penicillin G(7)between 1942-1944 there was a worldwide endeavor to discover new antibiotics from microorganisms and bioactive natural products [39,40].Up until 1968,old methods for detecting B-lactams were still being utilized and it was concluded that all natural B-lactams had been discovered [39].Nevertheless,this was not the case as with the introduction.in the 1970s.of new screening methods.the production of bacterial strains supersensitive to B-lactams,tests for the inhibition of B-lactamases and specificity for sulphur- containing metabolites resulted in the discovery of novel antibiotic structural classes (norcardicins carbapenems and monobactams)including the isolation of the antibiotics.norcardicin (8).imipenem (9)and aztreonam (10),respectively (Figure 2)[39,41].There are presently nine B-lactams (two cephalosporins,six carbapenems and one penem)in clinical trials or undergoing drug registration, along with the novel class of broad spectrum antibiotics called the glycylcyclines [41]. Figure 2.Penicillin(7),Norcardicin(8),Imipenem(9)and Aztreonam(10). NOHH OH -OH 01 7 H H CHa COOH N.SO3H HO Macro fungi such as polypores are a large group of wood-rotting fungi of the phylum Basidiomycota (basidomvcetes)and Ascomycota.which are a major source of pharmacologically active substances There are about 25,000 species of basidiomycetes,of which about 500 are members of the Aphyllophorales [42].Approximately 75%of tested polypore fungi have shown strong antimicrobial activities and may constitute a viable source for the development of novel antibiotics.Many compounds have displayed antiviral,cytotoxic,antineoplastic,cardiovascular,anti-inflammatory. immune-stimulating and anticancer activities [42,43].Fungi are more commonly microorganisms, some of which can spend at least part of their life cycle inside plant tissues without causing any visible
Metabolites 2012, 2 308 Undoubtedly one of the most famous natural product discoveries derived from a fungus (microorganism) is that of penicillin (7) from the fungus, Penicillium notatum discovered by Fleming in 1929 [33]. A countercurrent extractive separation technique which produced 7 in high yields was required for the in vivo experimentation that ultimately saved countless lives and won Chain and Florey (together with Fleming) the 1945 Nobel prize in Physiology and Medicine (Figure 2) [34]. This discovery led to the re-isolation and clinical studies by Chain, Florey and co-workers in the early 1940s and commercialization of synthetic penicillins, which ultimately revolutionized drug discovery research [35–38]. After publication of the first clinical data on penicillin G (7) between 1942–1944 there was a worldwide endeavor to discover new antibiotics from microorganisms and bioactive natural products [39,40]. Up until 1968, old methods for detecting β-lactams were still being utilized and it was concluded that all natural β-lactams had been discovered [39]. Nevertheless, this was not the case as with the introduction, in the 1970s, of new screening methods, the production of bacterial strains supersensitive to β-lactams, tests for the inhibition of β-lactamases and specificity for sulphurcontaining metabolites resulted in the discovery of novel antibiotic structural classes (norcardicins, carbapenems and monobactams) including the isolation of the antibiotics, norcardicin (8), imipenem (9) and aztreonam (10), respectively (Figure 2) [39,41]. There are presently nine β-lactams (two cephalosporins, six carbapenems and one penem) in clinical trials or undergoing drug registration, along with the novel class of broad spectrum antibiotics called the glycylcyclines [41]. Figure 2. Penicillin (7), Norcardicin (8), Imipenem (9) and Aztreonam (10). N N S O O H N N O O CO2H H H OH H NOH O CO2H H2N N O COOH HO S N H H H N H O N O SO3H 7 9 10 O 8 OH NH CH3 N N S H2N HO O O Macro fungi such as polypores are a large group of wood-rotting fungi of the phylum Basidiomycota (basidomycetes) and Ascomycota, which are a major source of pharmacologically active substances. There are about 25,000 species of basidiomycetes, of which about 500 are members of the Aphyllophorales [42]. Approximately 75% of tested polypore fungi have shown strong antimicrobial activities and may constitute a viable source for the development of novel antibiotics. Many compounds have displayed antiviral, cytotoxic, antineoplastic, cardiovascular, anti-inflammatory, immune-stimulating and anticancer activities [42,43]. Fungi are more commonly microorganisms, some of which can spend at least part of their life cycle inside plant tissues without causing any visible
Metabolites 2012.2 309 sign of infection or disease [44,45].They have been found to inhabit trees,grasses,algae and herbaceous plants and live in the intercellular spaces of plant stems,petioles,roots and leaves withou affecting the host organism [46].Collectively these fungi are known as endophytes.Novel bioactive secondary metabolites derived from fungal sources have yielded some of the most important natural products for the pharmaceutical industry [3]. In 1953.Edmund Kornfeld first isolated vancomycin(11)a glycopeptide antibiotic produced in cultures of Amycolatopsis orientalis which is active against a wide range of gram-positive organisms such as Staphvlococci and Streptococci and against gram-negative bacteria,mycobacteria and fungi and was approved by the FDA in 1958(Figure 3).It is used for the treatment of severe infection and against susceptible organisms in patients hypersensitive to penicillin (7)[5].The macrolide erythromycin (12)from Saccharopolyspora ervthraea is an antibacterial drug.which contains a 14-membered macrocycle composed entirely of propionate units(Figure 3).Erythromycin (12)has broad spectrum activities against gram-positive cocci and bacilli and is used for mild to moderate. upper and lower respiratory tract infections [5,26].Currently there are three semisynthetic ketolide derivatives of erythromycin (12).cethromycin (ABT-773.RestanzaTM).EP-420 (by Enanta Pharmaceuticals)and BAL-19403(by Basilea)which are in clinical development [1]. Figure 3.Vancomvcin (11)and Erythromvcin (12). 9 -C OH CH HOOC NH OH 11 Single cell viruses represent the smallest existing life forms causing cold,influenza,ebola and SARS.Presently,there seems to be a limited number of antiviral natural products or synthetically derived analogues from fungi [47].Betulinic acid (13),a triterpenoid obtained from the bark of Betula pubescens was originally identified as a weak inhibitor of HIV replication [48,49].Betulinic acid can inhibit topoisomerase I and is being evaluated in Phase I trials as a cancer chemo-preventive agent (Figure 4)[50].Bevirimat (PA-457)(14),extracted from a Chinese herb Syzygium claviflorum is in Phase IIb clinical trials and is believed to inhibit the final step of the HIV Gag protein processing [51] Ganoderic acid B(15),isolated from the fruiting bodies and spores of Ganoderma lucidum,displayed significant anti-HIV-1 protease activity with an ICso value of 20 uM (Figure 4)[52]
Metabolites 2012, 2 309 sign of infection or disease [44,45]. They have been found to inhabit trees, grasses, algae and herbaceous plants and live in the intercellular spaces of plant stems, petioles, roots and leaves without affecting the host organism [46]. Collectively these fungi are known as endophytes. Novel bioactive secondary metabolites derived from fungal sources have yielded some of the most important natural products for the pharmaceutical industry [3]. In 1953, Edmund Kornfeld first isolated vancomycin (11) a glycopeptide antibiotic produced in cultures of Amycolatopsis orientalis which is active against a wide range of gram-positive organisms such as Staphylococci and Streptococci and against gram-negative bacteria, mycobacteria and fungi and was approved by the FDA in 1958 (Figure 3). It is used for the treatment of severe infection and against susceptible organisms in patients hypersensitive to penicillin (7) [5]. The macrolide erythromycin (12) from Saccharopolyspora erythraea is an antibacterial drug, which contains a 14-membered macrocycle composed entirely of propionate units (Figure 3). Erythromycin (12) has broad spectrum activities against gram-positive cocci and bacilli and is used for mild to moderate, upper and lower respiratory tract infections [5,26]. Currently there are three semisynthetic ketolide derivatives of erythromycin (12), cethromycin (ABT-773, Restanza™), EP-420 (by Enanta Pharmaceuticals) and BAL-19403 (by Basilea) which are in clinical development [1]. Figure 3. Vancomycin (11) and Erythromycin (12). Single cell viruses represent the smallest existing life forms causing cold, influenza, ebola and SARS. Presently, there seems to be a limited number of antiviral natural products or synthetically derived analogues from fungi [47]. Betulinic acid (13), a triterpenoid obtained from the bark of Betula pubescens was originally identified as a weak inhibitor of HIV replication [48,49]. Betulinic acid can inhibit topoisomerase I and is being evaluated in Phase I trials as a cancer chemo-preventive agent (Figure 4) [50]. Bevirimat (PA-457) (14), extracted from a Chinese herb Syzygium claviflorum is in Phase IIb clinical trials and is believed to inhibit the final step of the HIV Gag protein processing [51]. Ganoderic acid β (15), isolated from the fruiting bodies and spores of Ganoderma lucidum, displayed significant anti-HIV-1 protease activity with an IC50 value of 20 µM (Figure 4) [52]
Metabolites2012.2 310 Figure 4.Betulinic acid (13).Bevirimat (PA-457)(14)and Ganoderic acid B(15) HO 13 In 2002,amrubicin hydrochloride(16),related to the anthracycline,doxorubicin(17)(Adriamycin), was isolated from the fungus Streptomyces peucetius.Doxorubicin (17)is used to treat acute leukaemia,soft tissue and bone sarcomas,lung cancer,thyroid cancer and both Hodgkins and non-Hodgkins lymphomas (Figure 5)[5.26].Torrevanic acid (18)was isolated from an endophvte from the endangered tree,Torreya laxifolia [53]and was tested in several cancer cell lines and found to display 5-10 times greater potentency/cytotoxicity in cell lines that are sensitive to protein kinaseC causing cell death by apoptosis(Figure 5)[54]. Figure 5.Amrubicin hydrochloride(16),Doxorubicin(17)and Torreyanic acid(18). OH HO.C NH CH. H 00H6 H CH OH 。 17 2.2.Natural Products from Plants Plants have been well documented for their medicinal uses for thousands of years.They have evolved and adapted over millions of years to withstand bacteria,insects,fungi and weather to produce unique.structurally diverse secondary metabolites.Their ethnopharmacological properties have been used as a primary source of medicines for early drug discovery [55,56].According to the World Health Organization (WHO).80%of people still rely on plant-based traditional medicines for primary health care [57]and 80%of 122 plant derived drugs were related to their original ethnopharmacological purpose [58].The knowledge associated with traditional medicine (complementary or alternative herbal products)has promoted further investigations of medicinal plants as potential medicines and has led to the isolation of many natural products that have become well known pharmaceuticals. The most widely used breast cancer drug is paclitaxel(Taxol)(19),isolated from the bark of Taxus brevifolia (Pacific Yew).In 1962 the United States Department of Agriculture (USDA)first collected the bark as part of their exploratory plant screening program at the National Cancer Institute
Metabolites 2012, 2 310 Figure 4. Betulinic acid (13), Bevirimat (PA-457) (14) and Ganoderic acid β (15). In 2002, amrubicin hydrochloride (16), related to the anthracycline, doxorubicin (17) (Adriamycin®), was isolated from the fungus Streptomyces peucetius. Doxorubicin (17) is used to treat acute leukaemia, soft tissue and bone sarcomas, lung cancer, thyroid cancer and both Hodgkins and non-Hodgkins lymphomas (Figure 5) [5,26]. Torreyanic acid (18) was isolated from an endophyte from the endangered tree, Torreya taxifolia [53] and was tested in several cancer cell lines and found to display 5–10 times greater potentency/cytotoxicity in cell lines that are sensitive to protein kinase C causing cell death by apoptosis (Figure 5) [54]. Figure 5. Amrubicin hydrochloride (16), Doxorubicin (17) and Torreyanic acid (18). 2.2. Natural Products from Plants Plants have been well documented for their medicinal uses for thousands of years. They have evolved and adapted over millions of years to withstand bacteria, insects, fungi and weather to produce unique, structurally diverse secondary metabolites. Their ethnopharmacological properties have been used as a primary source of medicines for early drug discovery [55,56]. According to the World Health Organization (WHO), 80% of people still rely on plant-based traditional medicines for primary health care [57] and 80% of 122 plant derived drugs were related to their original ethnopharmacological purpose [58]. The knowledge associated with traditional medicine (complementary or alternative herbal products) has promoted further investigations of medicinal plants as potential medicines and has led to the isolation of many natural products that have become well known pharmaceuticals. The most widely used breast cancer drug is paclitaxel (Taxol®) (19), isolated from the bark of Taxus brevifolia (Pacific Yew). In 1962 the United States Department of Agriculture (USDA) first collected the bark as part of their exploratory plant screening program at the National Cancer Institute
Metabolites 2012.2 311 (NCI)(Figure 6)[59].The bark from about three mature 100 year old trees is required to provide I gram of 19 given that a course of treatment may need 2 grams of the drug.Current demand for 19 is in the region of 100-200 kg per annum (i.e.,50,000 treatments/year)and is now produced synthetically [26]. The first of several FDA approvals for various uses for Taxol was announced in 1992 [60].Taxol (19)is present in limited quantities from natural sources,its synthesis(though challenging and expensive)has been achieved [61].Baccatin III(20)present in much higher quantities and readily available from the needles of T.brevifolia and associated derivatives is an example of a structural analogue that can be efficiently transformed into 19(Figure 6)26. Figure 6.Paclitaxel (Taxol)(19)and baccatin III(20). 0 H 19 Other examples of antitumor compounds currently in clinical trials include ingenol 3--angelate (21)a derivative of the polyhydroxy diterpenoid ingenol isolated from the sap of Euphorbia peplus(known as "petty spurge"in England or"radium weed'in Australia)which is a potential chemotherapeutic agent for skin cancer is currently under clinical development by Peplin Biotech for the topical treatment of certain skin cancers (Figure 7)[62.63].PG490-88(22) (14-succinyl triptolide sodium salt),a semisynthetic analogue of triptolide is a diterpene-diepoxide isolated from which is used for autoimmune and inflammatory diseases in the People's Republic of China [64,65].Combretastatin A-4 phosphate(23)a stilbene derivative from the South African Bush Willow,Combretum caffrum acts as an anti-angiogenic agent causing vascular shutdowns in tumors(necrosis)and is currently in Phase II clinical trials(Figure 7)[66.67]. Figure 7.ingenol 3-0-angelate(21),PG490-88(22)and Combretastatin A-4 phosphate(23) 21 The Acquired Immune Deficiency Syndrome (AIDS)pandemic in the 1980s forced the National Cancer Institute(NCI)and other organizations to explore natural products as sources of potential drug
Metabolites 2012, 2 311 (NCI) (Figure 6) [59]. The bark from about three mature 100 year old trees is required to provide 1 gram of 19 given that a course of treatment may need 2 grams of the drug. Current demand for 19 is in the region of 100–200 kg per annum (i.e., 50,000 treatments/year) and is now produced synthetically [26]. The first of several FDA approvals for various uses for Taxol® was announced in 1992 [60]. Taxol® (19) is present in limited quantities from natural sources, its synthesis (though challenging and expensive) has been achieved [61]. Baccatin III (20) present in much higher quantities and readily available from the needles of T. brevifolia and associated derivatives is an example of a structural analogue that can be efficiently transformed into 19 (Figure 6) [26]. Figure 6. Paclitaxel (Taxol®) (19) and baccatin III (20). Other examples of antitumor compounds currently in clinical trials include ingenol 3-O-angelate (21) a derivative of the polyhydroxy diterpenoid ingenol isolated from the sap of Euphorbia peplus (known as “petty spurge” in England or “radium weed” in Australia) which is a potential chemotherapeutic agent for skin cancer is currently under clinical development by Peplin Biotech for the topical treatment of certain skin cancers (Figure 7) [62,63]. PG490-88 (22) (14-succinyl triptolide sodium salt), a semisynthetic analogue of triptolide is a diterpene-diepoxide isolated from Tripterygium wilfordii which is used for autoimmune and inflammatory diseases in the People’s Republic of China [64,65]. Combretastatin A-4 phosphate (23) a stilbene derivative from the South African Bush Willow, Combretum caffrum acts as an anti-angiogenic agent causing vascular shutdowns in tumors (necrosis) and is currently in Phase II clinical trials (Figure 7) [66,67]. Figure 7. ingenol 3-O-angelate (21), PG490-88 (22) and Combretastatin A-4 phosphate (23). HO O O OH O OH 21 O O O O OPO3 23 O O O O O H O O O O Na 22 The Acquired Immune Deficiency Syndrome (AIDS) pandemic in the 1980s forced the National Cancer Institute (NCI) and other organizations to explore natural products as sources of potential drug
Metabolites 2012.2 312 candidates for the treatment of AIDS.Over 60,000 extracts of plants and marine organisms were tested against lymphoblastic cells infected with HIV-1.The most important result of these tests is the class of compounds known as the calanolides.In particular the isolation of calanolide a (24)and calanolide b (25)from the Calonphyllum species,along with prostratin (26)from Homalanthus mtans,have now progressed into clinical and preclinical development (Figure 8)[68-70].Calanolide A (24)was licensed and evaluated to Phase II clinical trials by Sarawak Medichem Pharmaceuticals,however there has been no subsequent announcement for further drug development.In 2010.Phase I human clinical trials of prostratin (26)were carried out by the AIDS ReSearch Alliance in Los Angeles, California(Figure 8). Figure 8.Calanolide A(24),Calanolide B(25)and Prostratin(26). HO Arteether (27),introduced in 2000,as Artemotil is derived from artemisinin(28)(introduced in 1987 as Artemisin)which was first isolated from the plant Artemisia annua and are both approved antimalarial drugs (Figure 9)[47].The plant was originally used in traditional Chinese medicine as a remedy for chills and fevers.Other derivatives of artemisinin (28)are in various stages of clinical development as antimalarial drugs in Europe [3,26].To date,a synthetic trioxolane modeled on the 28 pharmacophore,is being assessed in combination with piperaquine (a synthetic bisquinoline antimalarial drug)in an effort to treat malaria(Figure 9)[71]. Figure 9.Arteether(27)and artemisinin(28) H H H Grandisines A (29)and B(30)are two indole alkaloids which were isolated from the leaves of the Australian rainforest tree,Elaeocarpus grandis (Figure 10).Grandisine A (29)contains a unique tetracyclic skeleton,while Grandisine B(30)possesses an unusual combination of isoquinuclidinone and indolizidine ring systems.Both 29 and 30 exhibit binding affinity for the human 6-opioid receptor
Metabolites 2012, 2 312 candidates for the treatment of AIDS. Over 60,000 extracts of plants and marine organisms were tested against lymphoblastic cells infected with HIV-1. The most important result of these tests is the class of compounds known as the calanolides. In particular the isolation of calanolide A (24) and calanolide B (25) from the Calonphyllum species, along with prostratin (26) from Homalanthus nutans, have now progressed into clinical and preclinical development (Figure 8) [68–70]. Calanolide A (24) was licensed and evaluated to Phase II clinical trials by Sarawak Medichem Pharmaceuticals, however there has been no subsequent announcement for further drug development. In 2010, Phase I human clinical trials of prostratin (26) were carried out by the AIDS ReSearch Alliance in Los Angeles, California (Figure 8). Figure 8. Calanolide A (24), Calanolide B (25) and Prostratin (26). Arteether (27), introduced in 2000, as Artemotil is derived from artemisinin (28) (introduced in 1987 as Artemisin) which was first isolated from the plant Artemisia annua and are both approved antimalarial drugs (Figure 9) [47]. The plant was originally used in traditional Chinese medicine as a remedy for chills and fevers. Other derivatives of artemisinin (28) are in various stages of clinical development as antimalarial drugs in Europe [3,26]. To date, a synthetic trioxolane modeled on the 28 pharmacophore, is being assessed in combination with piperaquine (a synthetic bisquinoline antimalarial drug) in an effort to treat malaria (Figure 9) [71]. Figure 9. Arteether (27) and artemisinin (28). Grandisines A (29) and B (30) are two indole alkaloids which were isolated from the leaves of the Australian rainforest tree, Elaeocarpus grandis (Figure 10). Grandisine A (29) contains a unique tetracyclic skeleton, while Grandisine B (30) possesses an unusual combination of isoquinuclidinone and indolizidine ring systems. Both 29 and 30 exhibit binding affinity for the human δ-opioid receptor