SCIENCE/TECHNOLOGY
Largest Hydrocarbon Molecules Have Rigid Dendritic Structures up to, say, 50,000 atomic mass units. Liv ing organisms routinely synthesize giant biomolecules with tightly controlled structures and conformations. The syn thetic capability of chemists, by compar ison, is not as well developed, especially when the goal is to make molecules not found in nature. Traditional synthetic chemists have focused their efforts on molecules smaller than 2000 amu. And polymer chemists have concentrated on making macromolecules with veiy high molecular weights. But the midsized range—between, say, 2000 and 50,000 amu—has been neglected by organic chemists, Moore tells C&EN. In the mid-1980s, Mark C. Whiting and coworkers at the University of Bris tol in England explored the low end of this midsized range. They prepared par affins having as many as 390 carbon at oms and with molecular weights up to about 5500 amu. Those molecules, though, were linear chains. "This size regime [between 2000 and 50,000 amu] is rich and diverse" in its possibilities for molecular architectures, Moore says. "If s a size regime that I be lieve can ultimately produce functional molecules"—that is, molecules that
could be useful for catalysis, selective binding, electron transfer, energy con version, sensing, or other functions. The dendrimers prepared so far in Moore's lab, though, were not de signed to be functional. They are mere ly "scaffolding" to which functional groups could be attached in the future. One possibility Moore envisions is to arrange light-absorbing organic chroP6 mophores on the dendrimer skeleton and to use the resulting "molecular an > tenna" to collect light photons, funnel their energy to a focal point, and con vert this energy into chemical energy. Ο But such applications are just specula tion. For now, it is the architecture of Ron Dagani, C&EN Washington these new macromolecules that is really interesting. Technically, they are called effrey S. Moore has apparently out tridendrons because they have three done himself. Earlier this year, the arms or branches radiating from the cen University of Michigan chemist tral core unit, a benzene ring. Each arm published a paper with coworker sprouts further branches as it extends Zhifu Xu announcing the synthesis and from the core. The branches are tipped characterization of the largest all-hydro with 3,5-di-terf-butylphenyl groups, carbon molecule ever made—C1134H1146 which ensure solubility. [Angew. Chem. Int. Ed. Engl, 32, 246 (1993)]. But as he informed his col The smaller of the two molecules, leagues at the recent American Chemical C1134H1146, consists of 94 phenylacetylene Society meeting in Denver, a subsequent monomers. (In polymer parlance, it is macromolecule prepared in his Ann Ar called a 94-mer.) It has a molecular weight bor lab—C1398H1278—surpasses his of 14,776 and is 5.5 ran in diameter. own record. C1398H1278, built from 127 monomer Each of these molecules is thus far units, has a molecular weight of the largest member of two closely re 18,054. With a diameter of 12.5ran,it lated families of stiff dendrimers is spatially the largest dendrimer ever (highly branched polymers) that are reported, Moore says. constructed from phenylacetylene In two-dimensional representa building blocks. This work, like that tions, these molecules look like frac from several other labs, demon tal snowflakes. But the 94-mer actu strates that increasingly complex ally is globular, with large voids and treelike structures can be readily as niches in its interior, Moore says. The sembled from simpler units in a 127-mer, whose interior brandies are stepwise manner (C&EN, Feb. 1, longer, has a much flatter, more page 28). The resulting structures are open architecture. It looks more like intriguing because they may offer a pancake, Moore remarks. new chemistries and new properties In spite of their high arene content for scientists to explore. and stiffness, these molecules are quite soluble in pentane at room Moore's particular interest is in temperature, thanks to the large developing synthetic tools that will Computer-generated model shows globular number of ferf-butyl groups on the enable chemists to precisely build architecture of the 94-mer. The areas in yellow are periphery. In fact, within any denmolecules with molecular weights accessible to solvent molecules
• Synthesizing these giant, nonnatural molecules is easier than characterizing them, researchers discover
J
26
APRIL 12,1993 C&EN
Dendrimers have phenylacetylene skeletons
94-mer
127-mer
drimer family, the larger the molecule is, the more soluble it becomes. As one reviewer of Moore's paper noted, this increasing solubility bodes wellforbuilding even larger nanoscale molecules. The dendrimers were prepared by postdoctoral associate Xu using palladium-catalyzed cross-coupling chemistry. In each synthesis, three identical monosubstituted acetylene units were coupled to a triiodo-substituted core unit. The 94mer, for instance, was produced by coupling three 31-mer acetylenes to 1,3,5-triiodobenzene. For the 127-mer, three 39mer acetylenes were hooked onto a more elaborate core unit, a decameric aryl alkynyl triiodide. Making these molecules is far easier than characterizing them, says Moore, an assistant professor of chemistry. "The synthetic tools are [more advanced than] the characterization tools, especially for nonnatural molecules." For example, because no mass spectrometry method provides parent peaks beyond 2000 amu, the researchers had to find other ways to determine each molecule's chemical structure. Unambiguous proof of the 94-mer's structure was obtained using proton nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The 127mer, though, has eludedrigorouscharacterization because the proton signals in its NMR spectrum overlap too much to allow unambiguous assignment Nevertheless, Moore says he's "very confident" that the 127-mei/s structure follows that of its smaller cousins, which have all been rigorously characterized. Efforts are now under way in Moore's lab to construct even larger hydrocarbon dendrimers. The hope is that their rigidity, large size, and unique architecture will offer unusual physical properties. For example, preliminary results indicate the 127-mer fluoresces brilliantly under ultraviolet irradiation. This is a consequence of its extended linear conjugation, Moore says. His group is exploring these and other properties with support from the National Science Foundation and 3M Co. If s too early to tell whether these dendritic hydrocarbons will have any practical applications. But Moore is sure of one thing: This work "is pushing the limits of where synthetic organic chemistry is currently capable of going in the nonnatural world." And to push those limits to the max, he suggests, it helps to 'let your imagination go." • APRIL 12,1993 C&EN 27
SCIENCE/TECHNOLOGY
Oxygenated fuel cost may outweigh effectiveness overall trend by the use of oxygenated fuel was observed. Anderson says that according to the emissions model, a 15 to 20% reduction H in levels of carbon monoxide by the special gasoline should have been obfi served. "If the effect had been even as large as 10%, it should have been d e Deborah Illman, C&EN Washington tected by our techniques," he claims. To Anderson, these results reaffirm Results presented by Colorado scienthat "assessments must be based on an tists at a Division of Environmental analysis of what actually happened in Chemistry symposium on alternative the atmosphere, not what was expected fuels and the environment suggest that to happen." the cost of oxygenated gasoline may outweigh its effectiveness. Ted W. Hollman, air pollution control specialist in the mobile sources program When Coloradans became the first in of the Colorado Department of Health, the nation ordered to use oxygenated says that in addition to vehicle emissions fuel in wintertime, the goal was to ditesting, monitoring of ambient air for minish the concentration of carbon carbon monoxide and other compounds monoxide in the atmosphere. But assois conducted throughout a network of ciate chemistry professor Larry G. monitoring stations in the Front Range. Anderson and colleagues at the UniThe computer modeling done is "anversity of Colorado, Denver, claim that chored to real data," he says. data collected at a downtown Denver location show that use of oxygenated Hollman says information about the fuel has had no statistically significant number and kinds of cars on the road, effect on atmospheric carbon monoxide their emissions profiles, and meteoroconcentrations and may actually inlogical data are among the inputs used crease levels of other pollutants such as in modeling studies, which attempt to formaldehyde. separate the effects of variables like weather in order to estimate the net Colorado's pollution-restraint rules change in carbon monoxide concentracover the period of November through tion in the atmosphere that results February each year. A program requirfrom use of oxygenated fuel. He says ing fuels to consist of oxygen-containmodel parameters are tested on past ing compounds during that period monitoring data. began in January 1988. The required percentage of oxygen by weight has Anderson acknowledges that the state gradually increased from 1.5%, when collects data—his own analysis uses the program started, to the current levsome of the state's observations—but differs on how the data should be analyzed. Furthermore, Anderson asserts that the vehicle emissions tests are not representative of real driving conditions and underestimate carbon monoxide emissions. For example, the output of carbon monoxide is greater in cold automobiles; and emission of carbon monoxide varies with changing conditions such as speed and acceleration rate. "There are large uncertainties in the modeling process," he says. Hollman agrees that emissions tests are not representative of all driving conditions, and that ways to improve the tests are being considered. "The tests don't include enough hard accelerations and cold starting," he says. If, as Anderson suggests, oxygenated Grosjean, Popp, and Anderson (from left) answer questions at ACS press conference el of 2.7%. The oxygenate mostly used in the Denver area is methyl terf-butyl ether (MTBE), says Anderson. Motorists in Colorado's Front Range area, which includes Denver, Colorado Springs, and Fort Collins, spend an estimated $14 million more per year for the special gasoline. According to Anderson, officials have estimated the effect of the program on atmospheric carbon monoxide concentration by extrapolating results of vehicle emissions tests, using a theoretical emissions model to calculate the overall reduction of carbon monoxide expected in the Denver atmosphere. Anderson says the assumptions in that model are inaccurate, and moreover, official assessments have failed to adequately incorporate real experimental data in their calculations. Anderson and coworkers analyzed carbon monoxide concentration data covering the period 1981 to 1991 from the downtown Denver Continuous Air Monitoring Program station, the site in Denver that most commonly violates the carbon monoxide air quality standard. Anderson says their analysis demonstrates the existence of a strong downward trend in ambient carbon monoxide concentration during that entire period, beginning well before use of oxygenated fuels was initiated. The 55% reduction of carbon monoxide observed during the period is a much larger reduction than that expected from the emissions model, and no statistically significant contribution to the
28
APRIL 12,1993 C&EN
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SCIENCE/TECHNOLOGY fuel use has contributed little to the downward trend in ambient carbon monoxide concentration, then what has caused the 55% reduction since 1981? Anderson credits the decrease to fleet turnover—replacement of old cars by new ones with cleaner burning engines. That position was echoed by an independent audit of the effectiveness of oxygenated fuels mandated by the Colorado legislature in 1989. The report, issued in December 1992, found that "the limited benefits from oxygenated fuels are decreasing as the average emissions from new cars decrease, and will continue to decrease as new cars replace older cars." Carol E. Lyons, senior air quality scientist of PRC Environmental Management Inc., the company retained by the Colorado state auditor to perform the audit, says that "the program contributes to a limited, temporary reduction in automobile emissions of carbon monoxide and hydrocarbons. The cost of the program is over $1000 per ton of carbon monoxide reduced. Approximately 40% of the reduction occurs in 10% of the vehicles—those with the highest emissions with or without oxygenated fuels," and most other cars showed very little or no emissions reduction. The net effect is that the majority of drivers are subsidizing carbon monoxide reductions in the small percentage of heavy carbon monoxide emitters. "The audit recommended that oxygenated fuels be supplemented and eventually replaced by a strategy that targets only the high-emitting cars and cleans them up," says Lyons. One way to do that was described at the Denver meeting by chemistry professor Donald H. Stedman and colleagues at the University of Denver. The researchers use remote infrared spectroscopy to measure carbon monoxide and hydrocarbons on the fly, as the pollutants are actually emitted from the tailpipes of cars driving down the highway. The measurement is fast and can even be done while a video camera captures a picture of the vehicle's license plate. Stedman asserts that proper vehicle maintenance for new and old cars alike, not use of oxygenated fuel, is the key to clean-burning, low-emissions automobiles. Besides paying more for the special gasoline, there may be other costs asso30
APRIL 12,1993 C&EN
ciated with the use of oxygenated fuels. For one thing, atmospheric aldehyde concentrations may be on the rise. Because emissions tests suggest that formaldehyde emissions increase by 15 to 75% with oxygenated gasoline (depending on the emissions control technology on the vehicle), Anderson's group began collecting formaldehyde and acetaldehyde air samples in December 1987. "We have collected one of the largest aldehyde data sets at a single location, and certainly the largest data set where oxygenated fuels have been used," he says. Anderson's data suggest that motor vehicles are spewing at least 2 tons of formaldehyde per day into the Denver atmosphere during the wintertime. "It's a higher concentration of formaldehyde than we expected. And because the levels are strongly correlated to carbon monoxide, it is very clear that motor vehicles must be the source," says Anderson. His group reports that maximum four-hour average concentrations of formaldehyde have reached as high as about 50 ppb during some winter days in Denver. Gordon E. Pierce, air pollution control specialist in the technical services program of the Colorado Department of Health, acknowledges that Anderson's aldehyde data set is extensive. Pierce has been involved in smaller aldehyde monitoring efforts by the Department of Health, but says the data are "limited and spotty," and no conclusions have been drawn regarding the effects of oxygenated fuel on atmospheric aldehyde concentrations. He says recent monitoring efforts were conducted from October 1988 to June 1989, and then again from October 1991 to September 1992, but because oxygenated fuel use was mandated by the federal government, the department "saw little point in continuing to monitor for aldehydes." Anderson contends that conclusions about the effectiveness of the fuel program must consider the effects on levels of other pollutants besides just carbon monoxide. The total impact on air quality should be evaluated, he says. Elsewhere, oxygenated fuels have also been found to elevate organic, carbonyl compounds in the atmosphere. Chemistry professor Carl J. Popp of New Mexico Institute of Mining & Technology, Socorro, reported at the meeting that data collected in the Albuquerque area
suggest organic acids, especially formic acid, have increased in the atmosphere there because of the use of ethanol as a gasoline additive. Popp further reports that the ratio of pollutant peroxyacetyl nitrate (PAN) to peroxypropionyl nitrate—a ratio thought to be indicative of anthropogenic sources of atmospheric organics—has risen in Albuquerque to a level comparable to that found in Rio de Janeiro, where alcohol fuel is used exclusively. Daniel Grosjean of DGA Inc., an environmental consulting firm based in Ventura, Calif., has studied the effects of ethanol fuel on Brazilian air quality. He says Brazil has the highest atmospheric aldehyde concentration in the world. Acetaldehyde is emitted directly from the tailpipe because of incomplete combustion of ethanol and also is formed in the atmosphere by photochemical oxidation of emitted alcohol. Acetaldehyde is a precursor to PAN—a phytotoxic and mutagenic compound as well as a severe eye irritant—which is observed at parts-per-billion levels in Rio de Janeiro. The possibility of health problems from direct exposure to MBTE in oxygenated fuels is another potential cost associated with the program. Health complaints by residents of Fairbanks, Alaska, led to a petition to the Environmental Protection Agency to waive the oxygenated fuel requirement there. Symptoms reported by residents included headaches, nausea, throat and eye irritation, dizziness, and disorientation. Last Dec. 11, Alaska Gov. Walter J. Hickel announced that Fairbanks was granted an exemption by EPA. John Manly, press secretary in the governor's office, said studies by the Centers for Disease Control confirmed the presence of MTBE in blood samples of residents reporting symptoms. "It didn't make sense to kill us with the cure," says Manly. Arco Chemical Co., a leading producer of MTBE, is joining with other producers of the additive and EPA to fund studies of commuter exposures to MTBE. Gerald T. Davis, manager of public relations at Arco Chemical, says MTBE is a thoroughly tested and safe product. "Objections to the odor [of MTBE] should not be confused with health effects," he says, but Arco is supporting additional studies because of concern about the reports. •
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FUNCTIONALIZED ORGANOZINC REAGENTS Br-Zn-(CH2)nCN
Cage molecules made in macroscopic amounts
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The carbon-metal cage molecules known as metallo-carbohedrenes, or "met-cars," have been produced in macroscopic amounts for the first time by a vaporization technique sim ilar to that used to produce bulk quantities of fullerenes. Although in dividual met-car species have not yet been isolated in pure form, the re search suggests that these molecules will be stable enough to isolate and characterize rigorously. The research on met-cars was de scribed by A. Welford Castleman Jr., a chemistry professor at Pennsylvania State University, University Park, at a symposium sponsored by the Division of Physical Chemistry. A report on pro ducing macroscopic amounts of met-
Mass spectra suggest 'met-cars' in soot Relative intensity
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APRIL 12,1993 C&EN 31
SCIENCE/TECHNOLOGY met-cars, Castleman and coworkcars also appeared in last week's ers Stephen F. Cartier, Ziyun Y. Science [260,195 (1993)]. Chen, Gerhard J. Walder, and Castleman and coworkers disCalvin R. Sleppy modified the arccovered met-cars last year in exdischarge technique developed for periments in which they used a the production of fullerenes. The laser to vaporize titanium into a chemists use metal-graphite comhelium gas stream that contained posite electrodes in a discharge reone of a number of simple hydroaction chamber through which hecarbons. The mass spectrum of lium flows. An electric arc between the products that emerged from the sharpened electrodes creates a this plasma contained a single, plasma. prominent peak. Isotopic substitution experiments using deuterated After the plasma is terminated, hydrocarbons and hydrocarbons the chemists collect the deposited containing carbon-13 atoms estabblack soot from the surfaces of the lished the species as Ti8C12. reaction chamber and analyze its contents by time-of-flight mass Based on their experimental respectrometry. A typical mass specsults, the Penn State chemists proComputer graphic depicts idealized pentagonal trum of the soot produced from a posed a pentagonal dodecahetitanium-graphite electrode condron structure for Ti8C12. This is a dodecahedron structure of Ti8C12, titanium atoms are shown in purple, carbon atoms in green tains a prominent peak at 528 cage made up of 12 pentagons, atomic mass units, corresponding each of which contains two titanium and three carbon atoms. Each tita- other early transition metals, including to Ti8C12, and a much smaller peak that nium atom bonds to three carbon at- vanadium, hafnium, and zirconium, corresponds to Cœ. oms, and each carbon atom binds to an also form met-cars, although not so Soot generated from a vanadiumadjacent carbon and two titanium at- readily as titanium. graphite electrode analyzed in the oms. The researchers also showed that To produce macroscopic amounts of same manner contains a prominent
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CAS DOS covers ΜΤ in learning the DNA rec Bn ,0-CH,ognition and binding func L °Γ tions of oligosaccharides has been the difficulty in making these exotic sugars. Ι OBn Kahne has improved this situation by devising a onepot synthesis of the trisac charide side chain of dclamycin. molecules of chromomycin and a mag The trick is to string together the so- nesium ion. Kahne said in Denver that, with called A, B, and C pyranose rings of the sugar chain in correct order. Kahne used magnesium, the chromomycin agly reactions in which the hydroxyl group cone forms only a 1:1 complex, but the on one pyranose ring attacked an acti complete molecule forms a 2:1 com vated phenyl sulfoxide leaving group on plex, just as is observed in DNA bind ing. Moreover, between the two side the aldehyde carbon of another. With three reactants in the same pot, chains, only the trisaccharide seems the Princeton worker had to fine-time important for dimerization, because the reactivity of phenyl sulfoxides so dimerization still occurs even if chro that they would be displaced in the momycin lacks the disaccharide chain. Stephen Stinson correct order. Activation of sulfoxides was by reaction with trifluoromethanesulfonic acid, which chemists have nicknamed triflic acid. Triflic acid acti vation occurs faster at electron-rich centers. So Kahne made the first of the intended string with a group p-methoxyphenyl sulfoxide. The next in line bore an unsubstituted phenyl sulfox ide. With the building blocks so tuned > in advance, the reaction cleanly yielded the correct trisaccharide. Chromomycin is yet another com pound in which an oligosaccharide side chain is important to DNA bind Air Products & Chemicals has devel ing. Previous investigators had shown oped a new family of catalysts, based that the compound without its two car on using methane in the presence of bohydrate chains, called an aglycone, oxygen, that effectively reduce nitrogen did not bind DNA. It was also known oxides in combustion exhaust streams. that the bound complex contained two This new chemistry offers an effective 3
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APRIL 12,1993 C&EN
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ρ-
Catalyst cuts nitrogen oxides using methane
alternative to existing, and more ex- are produced in combustion of fuels Products, and coworker Yuejin Li told containing chemically bound nitrogen the symposium that the new family of pensive, precious-metal catalysts. The new catalytic approach, de- along with molecular nitrogen from air. catalysts overcomes most of the probscribed at a Catalysis & Surface Science All other oxides of nitrogen originate lems. The catalysts can, for example, efSecretariat symposium, uses metal- with the formation of nitric oxide, which fectively reduce nitrogen oxide with exchanged crystalline zeolites and can be rapidly oxidized with ozone, OH" methane in the presence of excess molecmethane as the reducing agent. The ex- or H0 2 radicals. If nitric oxide can be pre- ular oxygen, permitting the complete rechanged metals include cobalt, nickel, vented from entering the atmosphere, duction of nitric oxide at 400 °C over a iron, chromium, and manganese. How- most of the other forms of nitrogen oxide Co-ZSM-5 catalyst. The chemistry likely to be involved under these conditions is: ever, cobalt appears to be the most ef- can be correspondingly eliminated. fective in reducing nitrogen oxides. Methane is among the reductants that 2NO + CH4 + 0 2 - * N 2 + 2H 2 0 + C0 2 Nitrogen oxide emissions have been have been considered for catalytic proCH4 + 20 2 ->2H 2 0 + C0 2 identified as possible causes of smog in cesses because it is abundant in most According to Armor, the significant urban and industrial areas, acid rain, combustion plants. The problem with and numerous adverse effects on human methane is that it reacts much faster feature of this chemical system is the health. About 55% of the nitrogen oxide with oxygen than with nitric oxide at the ability of the catalysts to carry out the emissions in the U.S. come from station- usual temperatures found in most com- first reaction while minimizing the secary combustion boilers, particularly bustion processes and with most cata- ond. All the catalysts reported by Arthose used for electric power generation. lysts. Also, in the presence of oxygen, a mor are zeolites exchanged with nonOther sources include automobiles, in- considerable excess of methane is re- precious metals. Until now, Armor dustrial and commercial boilers, and quired to maintain a reducing environ- says, nitric oxide has never been found ment. A major concern has been that ef- to be selectively reduced by methane in home-heating units. Three major technologies to reduce fective catalysts are often precious met- the presence of excess oxygen at meththe concentrations of nitrogen oxide in als that are not usually of sufficient ane levels below 2000 ppm. Without oxygen the nitric oxide conexhaust streams have been tried. One selectivity to be of commercial interest. technique has been to modify the fuel John N. Armor, principal research as- version was only about 17%. With the adbefore combustion. Another approach sociate in catalysis and adsorbents at Air dition of 0.5 mole-% oxygen, the converhas been to modify the combustion process itself to minimize the production of nitrogen oxides. Probably the most successful method however, has been to remove nitrogen oxides from the flue gases. Of the flue gas treatments, selective catalytic reduction (SCR) of nitrogen oxides has been in use for about 20 years and appears to be the most selective for We're dedicated to Sodium Lactate nitrogen oxide reduction. Even so, the present state of SCR technology is insufA new dedicated facility for the production of ficient to meet new requirements of the Sodium Lactate and other Lactate Salts to meet Environmental Protection Agency. the growing market for these products was SCR is typically carried out using ambrought on stream March 1, 1992. Approximately monia as a reductant and a titaniasupported vanadia catalyst at tempera20,000 square feet of new capacity has been tures up to 400 °C. The chemistry of this constructed for the manufacture of these basic process is complex, and there has been a products under GMP conditions for use in pharprolonged effort to improve the process by replacing ammonia as the reductant. maceutical, food, and cosmetic applications. One attractive possibility is to replace Contact us today for more information and a catammonia with a hydrocarbon, specifialog. cally methane. At best, the effort has met with only modest success. PFANSTIEHL LABORATORIES, INC. Other attempts at catalytic reduction The source for carbohydrate chemistry of nitrogen oxides were made by Japanese researchers during the 1980s. They 1219 Glen Rock Avenue/Waukegan, IL 60085-0439 Tel.:1-708/623-0370/TollFree:1-800/383-0126 used zeolites exchanged with transition FAX:708/623-9173 metals—for example, copper, chromi99-P um, nickel, iron, and manganese—but they did not use methane as a reductant, as does the new Air Products system. Nitrogen oxide consists primarily of nitric oxide and nitrogen dioxide, which
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APRIL 12,1993 C&EN 35
SCIENCE/TECHNOLOGY sion increased to 60%. More oxygen did not increase the conversion. Thus, Armor says, Co-ZSM-5 has been established as a nitrogen oxide reduction catalyst. Nitric oxide reduction is proportion al to the partial pressure of methane in the system. The conversion approaches 100% when methane is present in con centrations of about 2000 ppm. Other catalytic materials found to be effective in this investigation include Cu-ZSM-5 and Cr-ZSM-5. Neither is as effective as Co-ZSM-5. Co-Y is also less effective than Co-ZSM-5 and CoO/ A1203 is almost inert for this chemistry. The great differences in the nitric oxide reduction for the various forms of co balt indicate the importance of the na ture of the support. Zeolites such as ZSM-5 correctly position the cobalt cat ion in its active state for the reaction. Armor and his associates are con tinuing the development of this catalyt ic system to optimize performance and to identify the design parameters of po tential commercial applications. Joseph Haggin
ChiraP93 2 day symposium - Chemical and Biotransformation routes to chiral compounds INCLUDES PAPERS BY Dr Colin Bayley, Dr Mark J. Burk, Dr Η Ρ Buser, Michael J Cannarsa, Dr Claude Chassin, Dr David L Coffen, Richard L DiCicco, Dr Michael Ρ Doyle, Professor Κ Drauz, Dr Paul van Eikeren, Professor R Gollamudi, Professor Tamio Hayashi, Dr Ivan Lantos, Dr Takehisa Ohashi, Professor Iwao Ojima, Dr Ν Pridgen, Dr X Radisson, Dr Terry L. Rathman, Dr Paul J. Reider, Dr Andy Richards, Professor Stanley Roberts, Professor Κ Barry Sharpless, Dr David Stirling, John Τ Talley, Dr Richard CTitmas, Timothy J Wozniak May 6-7th 1993 Hyatt Regency Hotel Reston, Virginia, USA For more details and booking contact: Brandon Associates PO Box 1244 Merrimack, NH 03054 USA Tel/Fax (603) 424-2035
New family of Taxol, Taxotere analogs developed >
Ο A new family of analogs of the antican cer agents Taxol and Taxotere was in troduced at a poster session in the Di vision of Medicinal Chemistry. The an alogs are derivatives of a hydroxylated taxane found in renewable yew nee dles. In in-vitro assays of activity with cancer cell lines, one of the analogs shows higher potency than Taxol against several types of cancer. The new drug candidates were dis covered by Young Hoon Park, ChungMing Sun, and Iwao Ojima in the de partment of chemistry of the State Uni versity of New York at Stony Brook, in collaboration with Giovanni Appendino and Ivana Finoglio of the depart ment of pharmaceutical science and technology of the University of Turin, Italy. Patents on the compounds have been applied for. Ojima points out that the analogs "are not real drugs yet. They have a long way to go. But they are showing quite encouraging basic results."
Taxotere analog is made from hydroxylated precursor HO
CIRCLE 3 8 ON READER SERVICE CARD
APRIL 12,1993 C&EN
HO
Ο OH
HOH°/°
HO
HO°
Ο OH
ΧΛ V USBOJ-Tax-1011
14-Hydroxy-10-deacetyIbaccatin III Ο OH
HO Ô
0\
10-DeacetyIbaccatin III Source: I. Ojima
36
Taxol, a Bristol-Myers Squibb prod uct, was originally made only from yew bark in a process that killed the trees, but is now increasingly being produced by semisynthesis from 10deacetylbaccatin III (10-DAB III), a tax ane found in yew needles. Taxotere, a Rhône-Poulenc Rorer drug, has always been manufactured by semisynthesis from 10-DAB III. The world's largest supplier of 10DAB ΙΠ is Indena, a natural products company in Milan, Italy. According to Ojima, Indena recently discovered 14hydroxy-10-deacetylbaccatin ΙΠ, a baccatin compound with an additional hydroxyl group, in extract from yew nee dles. Indena also has applied for patents on derivatives of the new taxane. Owing to the presence of the hydroxyl function, the 14-hydroxy com pound has higher water solubility than 10-DAB III. Analogs derived from the new taxane are also more water soluble than Taxol and Taxotere, a property that Ojima believes could make them potentially easier to administer. Low water solubility has been a problem with Taxol, making formulation of the drug difficult. Taxotere is a bit more water soluble than Taxol, but it "still has problems," says Ojima.
HO
ρ
OH
XA OH
HO 0=
Taxotere
Ρ °-
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ACS beams live seminar to Europe A presidential satellite television seminar held last month featured the American Chemical Society's first-ever live television broadcast to Europe. Speakers at the seminar on "Molecular Modeling in the Discovery of New Drugs" included (left to right): Michael D. Varney, director of medicinal chemistry at Agouron Pharmaceuticals; John J. Baldwin, distinguished senior scientist at Merck Laboratories; ACS president Helen M. Free, professional relations consultant for Miles Inc.; moderator Paul Anthony; Jonathan Greer, senior project leader and senior research fellow, Abbott Laboratories, who was the seminar's technical coordinator; and John W. Erickson, director of the structural biology program at the National Cancer Institute. In addition, Gerd Folkers and Didier Rognan of the department of pharmacy of the Swiss Federal Institute of Technology, and Peter Warner, principal medicinal chemist of Zeneca Pharmaceuticals, made live presentations from Europe. Almost 3000 scientists in the U.K., Sweden, and North America watched the seminar and participated in its question-and-answer sessions. "These seminars give scientists worldwide the opportunity to hear symposium-style presentations on the latest advances in modeling and also to participate in dynamic discussions with an international audience without having to travel around the globe," says Cyrelle K. Gerson, manager of ACS media courses.
Taxol- and Taxotere-like derivatives of 14-hydroxy-10-deacetylbaccatin III were synthesized by Ojima and coworkers, and were then tested on cancer cell lines by Ralph Bernacky and Paula Pera at the Roswell Park Cancer Institute, Buffalo, N.Y. One of the most promising analogs, called USBOJ-Tax-1011, is more than three times more active than Taxol against a human non-small-cell lung cancer cell line, and more than twice as active against a human colon cancer cell line. Analog 1011 also shows stronger antitumor activity than Taxol against human ovarian and breast cancer cell lines, including adriamycin-resistant breast cancer cells. The researchers haven't obtained any data yet on the anticancer activity of the analogs relative to that of Taxotere.
Because development of the analogs hadn't been disclosed before the ACS meeting, Ojima does not yet know if any drug companies will show interest in developing them. "Bristol-Myers Squibb and Rhône-Poulenc Rorer have made maybe hundreds of analogs of Taxol and Taxotere," says Ojima. "Nevertheless, I am quite sure they have not worked on 14-hydroxy analogs yet." The work could "open up a new avenue for the development of modified taxanes as anticancer drugs," Ojima says. He hopes the analogs will show activity against different cancers than Taxol and Taxotere show, or that they may have properties that mitigate or eliminate some of the undesirable side effects of the original drugs. Stu Borman
Helping Your Child Learn Science H
ere's a practical guide for stimulating a child's interest in science. Presenting safe and simple activities suitable for children from preschool through the early elementary grades, Helping Your Child Learn Science suggests activities with bubbles, bugs, plants, crystals, and television. Most of the activities cost little or nothing and require no special equipment. This handy volume explores opportunities for learning science in such places as zoos, museums, planétariums, aquariums, and farms. It presents definitions and descriptions of science and provides suggestions for helping children understand and learn scientific ideas. Appendices offer practical tips encouraging schools to develop good science programs, descriptions of nine scientific concepts, and a list of recommended science books and magazines. Originally available from the U. S. Department of Education. Nancy Paulu and Margery Martin 76 pages (1993) Paperbound ISBN 0-8412-2626-1 $11.95 O
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