by Dennis V.C. Awang, PhD, FCIC, and Mark Blumenthal

The incipient concern over an impending bird flu pandemic has fueled an almost desperate effort to secure supplies of the most promising oral antiviral against avian flu to date—Tamiflu® (oseltamivir). During last year’s influenza season, approximately 1.7 million prescriptions were written for oseltamivir in the United States, and according to the manufacturer, nearly twice as much of the drug was produced for this year’s season.¹

Tamiflu is part of a new class of medicines called neuraminidase inhibitors. The surface of an influenza virus contains neuraminidase proteins that enable new virus particles to bud on the surface of the host cell. The neuraminidase enzyme breaks the bonds that hold these new virus particles to the outside of an infected cell, setting them free to infect other cells and spread infection. Neuraminidase inhibitors block the enzyme’s activity and prevent new virus particles from being released, thereby limiting the spread of infection.²

The current sole manufacturer of Tamiflu, the Swiss-based Roche Pharmaceuticals, had previously suspended public sales of the drug in the wake of a widespread assault on pharmacy supplies. The company’s action is claimed justified on the basis of preserving supplies of the drug for governmental agencies and institutions caring for the most vulnerable patients. In the meantime, efforts are increasing to develop more efficient, cost-effective synthetic approaches to the drug.

In addition to announcing that it would increase its own production of Tamiflu, in December Roche stated that it would cooperate with a group of companies to produce higher quantities of the drug to meet increasing world demand.³

Currently the most satisfactory commercial route to the production of Tamiflu is based on extraction of shikimic acid from the fruits of Chinese star anise (Illicium verum Hook f., lliciaceae; bajiao in Mandarin). However, this plant, a small tree up to 10 meters tall, is notoriously difficult to cultivate and also matures at a very slow rate, flowering only after 6 years.⁴ Roche so far has commanded roughly 90% of the world’s supply of Chinese star anise, which is grown only in 4 Chinese provinces. Alarmingly, almost all of this year’s star anise crop has been reportedly destroyed by a series of mudslides produced by unseasonably severe tropical storms.⁵

Because the star anise connection as a starting material for the production of Tamiflu has some potential media value—i.e., the drug is based on a chemical derived from a traditional spice and medicinal plant—numerous articles have appeared in the mainstream media focusing on star anise and its relative scarcity in relation to the mushrooming demand for Tamiflu.^3,6 A report in the China Daily states that the price of star anise had almost doubled in one week in November. In Guangxi province, the price rose from 5 yuan (US $0.60) per kilogram to 8.2 yuan (US $1.00) per kilo, according to a wholesaler in Wuzhou, who reportedly had taken stock of 60 tons of the fruit, even before Roche had purchased available stocks.⁷ The New York Times reported in November that the cost of shikimic acid in China rose from $40 to over $400 per kilo.³

Shikimic acid is also a constituent of the toxic fruit of Japanese, or bastard, star anise, also called sacred anise (I. anisatum L.). This species, termed shikimi-no-ki in Japanese, is cultivated near Buddhist temples and used in religious ceremonies, such as branches for decorating graves.^4,8 The relative abundance of shikimic acid in the fruits of I. anisatum and I. verum, and any significant differences in ease of extraction, are not evident in the available literature. However, concern has been expressed regarding the adulteration of Chinese star anise with Japanese star anise, due to the documented neurologic and gastrointestinal toxicities of purported Chinese star anise tea administered to infants.^9,10 A rapid and efficient method for detecting I anisatum in I. verum powder has been recently published.¹¹ The procedure involves a combination of microscopy (fluorescence and scanning electron) and gas chromatography, which easily detects the presence of eugenol, methoxyeugenol, and 2,6-dimethoxy-4-allyphenol, compounds not present in I. verum. However, the distinction between these two species of Illicium is of concern primarily for the purpose of ensuring the purity of Chinese star anise for food use (e.g., herbal teas). For the production of shikimic acid suitable for synthetic production of oseltamivir, this distinction does not appear to be of significance as only the shikimic acid is isolated and purified for further chemical elaboration into oseltamivir.

Considerable interest has been expressed by reporters in the mistaken and dangerous belief that drinking star anise extracts can be an effective treatment for the avian flu (N.R. Farnsworth oral communication to D.V.C. Awang, November 4, 2005). However, neither such extracts nor shikimic acid itself and its metabolites have been demonstrated to have such efficacy. Expressing concerns about the misuse of star anise as an herbal preventive or treatment for avian flu, a coalition of herb and dietary supplement industry trade associations have stated categorically that such activity is not only not recommended but is strongly discouraged.¹²

Due to the initially high cost ($50 per gram) of research quantities of shikimic acid, Roche contracted with Michigan State University (MSU) scientist J. W. Frost to develop a fermentation process for production of (-)-shikimic acid. Frost discovered a strain of E. coli that overproduces the acid when fed glucose, which eventually led to bacterial growth on a commercial scale. Roche now obtains large quantities (measured in tons) of shikimic acid both by fermentation and star anise fruit extraction, but isolation and purification are time-consuming.¹³

The current semi-synthetic manufacture of Tamiflu from shikimic acid is a complex, time-consuming, 10-step process, involving potentially explosive azide chemistry. Roche claims that from raw material sourcing to production of Tamiflu capsules takes a complete year. Shikimic acid is first converted to a diethyl ketal intermediate, which is then reduced in 2 steps to an epoxide that is finally transformed to Tamiflu in 5 subsequent steps, 3 of which involve highly toxic explosive azide intermediates.¹³ Despite this apparent complexity, it was reported in the November 3rd edition of the Wall Street Journal Asia¹⁴ that Roche’s claim as to the difficulty of producing Tamiflu is greatly exaggerated. Rather than the claimed full year required for synthesis from shikimic acid, Taiwan’s National Health Research Institutes claims to have produced a small quantity of the antiviral in 18 days! Also, Cipla Ltd., an Indian generic drug manufacturer, claims to have been successful in a pilot phase production of the drug.¹⁴ However, these relatively small-scale productions can be expected to be much less time-consuming than large-scale manufacture under good manufacturing practices (GMPs).

Roche and MSU scientist Frost have explored chemical and microbial means to obviate azide intermediates: an azide-free allylamine route from epoxide to Tamiflu and microbial production of aminoshikimic acid as a starting material were developed. Also, two other routes that do not involve shikimic acid have been explored. However, so far, no alternative has been found to surpass the shikimic acid-azide commercial route in terms of cost and efficiency.¹³

Perhaps future chemical synthetic innovation and/or a lower-cost, more productive source of shikimic acid will satisfy the urgent demand for increased supplies of Tamiflu. In the meantime, doctors have discovered that teaming Tamiflu with a low-cost generic drug used in World War II to extend scarce supplies of penicillin, doubles the antiviral’s effectiveness: the “helper” drug probenecid reduces Tamiflu excretion in urine, thereby elevating blood levels roughly twofold.¹⁵

Recently, the Canadian generic drug manufacturer Biolyse Pharma Corp., which specializes in extracting chemicals from plants at its plant in St. Catharines, Ont., revealed plans to extract shikimic acid from Christmas trees.¹⁶ Extractable shikimic acid, reportedly constitutes 2 to 3% of the biomass from various pine spruce, and fir trees. The shikimic acid from this source will be considerably cheaper than its current price, which has soared to more than $500 (US) a kilogram from $45 over the past year due to shortages of Tamiflu and skyrocketing demand.

The question then arises as to how much Tamiflu can be produced from the scarce shikimic acid supplies. The New York Times article cites an unnamed Roche chemist who said that 13 grams of star anise could produce 1.3 grams of shikimic acid, which then could be used to make 10 Tamiflu capsules, the amount required to treat one person. Thus, one ton of shikimic acid could treat 770,000 people. However, the Times article also cites another expert, Y.K. Hamied, PhD, a chemist and Chairman of Cipla, who says that the figure was more realistically about 300,000 as newcomers to the Tamiflu production business would probably not be able to enjoy the production efficiencies currently attained by Roche. Other potential sources of shikimic acid reportedly considered by Gilead Sciences Inc. of Foster City, California, are cinchona bark (Cinchona spp., Rubiaceae, source of quinic acid, a precursor of shikimic acid), ginkgo trees (Ginkgo biloba L., Ginkgoaceae), and the needles of giant sequoias (Sequoiadendron giganteum [Lindl.] J. Buchholz, Cupressaceae).³

Dennis V. C. Awang, PhD, FCIC, is president of MediPlant Consulting, Inc., White Rock, BC, Canada, a natural products consulting group. Before retiring after 24 years at Health Canada, he was the Head of the Natural Products Section in the Bureau of Drug Research at the Canadian Health Protection Branch. He is currently revising the classic Herbs of Choice: The Therapeutic Use of Phytomedicinals (Haworth Press), initially authored by the late Professor Varro E. Tyler.

Mark Blumenthal is founder and executive Director of the American Botanical Council and Editor of HerbalGram.

References

1. Hayden FG. Antiviral resistance in influenza viruses — Implications for management and pandemic response. New Engl J Med. February 23, 2006;354:785-788.

2. Woods JM, Bethell RC, Coates JA, et al. 4-guanidino-2, 4-dideoxy-2, 3-dehydro-N-acetylneuraminic acid is a highly effective inhibitor both of the sialidase (neuraminidase) and of growth of a wide range of influenza A and B viruses in vitro. Antimicrob Agents Chemother. 1993;37(7):1473-1479.

3. Pollack A. Is bird flu drug really so vexing? Debating the difficulty of Tamiflu. New York Times, November 5, 2005. Available at: http://www.nytimes.com/2005/11/05/business/05tamiflu.html?ei=5070&en=e0d5349d5f7dd5ae&ex=1136350800&pagewanted=all.

4. Small E. Confusion of common names for toxic and edible “star anise” (Illicium) species. Econ Bot. 1996;50(3):337-339.

5. Slow-growing star anise wiped out by mudslides. Vancouver Sun. October 27, 2005.

6. Goodman PS. Star Rises in Fight Against Bird Flu. Washington Post. November 18, 2005.

7. Wang ZQ. Star anise soars to surprise fame. China Daily. November 2, 2005.

8. Hocking GM. A Dictionary of Natural Products. Medford, NJ: Plexus Publishing, Inc.; 1997:391.

9. Ize-Ludlow D, Ragone S, Bernstein JN, Bruck IS, Duchowny M, Garcia Pena BM. Chemical composition of Chinese star anise (Illicium verum) and neurotoxicity in infants. JAMA. 2004;291(5);562-563.

10. Ize-Ludlow D, Ragone S, Bruck I, Bernstein J, Duchowny M, Garcia Peña B. Neurotoxicities in Infants Seen With the Consumption of Star Anise Tea. Pediatrics. October 18, 2004; 114;653-656. Available at: http://www.pediatrics.org/cgi/content/full/114/5/e653.

11. Jashi VC, Srinivas PV, Khan IA. Rapid and easy identification of Illicum verum Hook. f. and its adulterant Illicium anisatum Linn. by fluorescent microscopy and gas chromatography. J AOAC Int. 2005;88(3):703-706.

12. Industry Coalition Advises Against Use of Dietary Supplements as Remedy for Avian Flu [press release]. American Herbal Products Association, Consumer Healthcare Products Association, Council for Responsible Nutrition, National Nutritional Foods Association, November 18, 2005.

13. Yarnell A. Complexity of Tamiflu manufacturing may hamper on demand production. Chem & Eng News. 2005; 83(35): 22-23.

14. Zamiska N, Dean J. Generics Challenge Roche’s Tamiflu Claims. Wall Street Journal. November 3, 2005.

15. Spears T. Generic ‘helper drug’ can stretch Tamiflu ingredient. National Post (Canada), November 2, 2005.

16. Zehr L. Christmas trees to provide key Tamiflu ingredient. The Globe and Mail (Toronto); December 2005:B3, 23.

Sidebar:
The Fermented Cabbage Connection

Recent Korean research has found that a culture filtrate of the bacterium Leuconostoc kimchi (prepared from the Korean spiced fermented cabbage dish kimchi), when administered to chickens infected with the bird flu virus, led to recovery of 11 of 13 birds. However, while surging sales of kimchi across Asia suggest that consumers believe that it may protect them against bird flu, the bacterial preparation has not yet been tested on bird flu in humans, even though it has shown a “very potent effect” against human flu in vitro.¹

Europeans claim that the Korean process for kimchi production is exactly the same as that for the popular European fermented cabbage dish sauerkraut, but the Korean researchers have stated that their research cannot be used to demonstrate similar benefits for sauerkraut, stressing that the antiviral effect of the bacterial product is “strain-specific.”¹

Reference

1. Patton D. Cabbage dish gaining popularity as flu-fighter. November 16, 2005. Available at: http://www.nutraingredients.com/news/ng.asp?n=63932-kimchi-sauerkraut-bird-flu.