NEWS OF THE WEEK SCIENCE
EXOTIC FULLERENE Synthesis of metallofullerene derivative brings medical applications closer
I
N 1999, CHEMISTRY PROFESSOR
Harry C. Dorn introduced the scientific world to an exotic new type of metal-containing fullerene: a C80 cage encapsulating a trimetallic nitride cluster such as Sc3N (C&EN, Sept. 20, 1999, page 54). Now, Dorn's group at Virginia Polytechnic Institute & State University, Blacksburg, has synthesized and characterized the first organic derivative of this cage complex [J.Am. Chem. Soc, 124,524 (2002)}. The achievement, he says, is "a major stepping stone" toward the preparation of functionalized endohedral metallofullerenes that could find use in the diagnosis and treatment of medical conditions. A fullerene containing gadolinium, such as Gd2ScN@C80, could provide an improved contrast-enhancing agent for magnetic resonance imaging (MRI) ofthe body And fullerenes encapsulating a radioactive atom such as holmium could be useful as tracers or anticancer agents. The problem with such metallofullerenes, though, is that they don't dissolve in aqueous fluids, so getting them into tissues is difficult. Functionalizing the cage complex with an organic group that can be made water soluble, however, would eliminate that difficulty That's what Dorn and his coworkers have done. The team prepares the metallofullerenes in an electric arc furnace by vaporizing, in the presence of nitrogen, a graphite rod packed with a powdered metal oxide such as Sc 2 0 3 . The desired product— Sc3N@C80—is separated from the C60- and C70- containing soot and is purified. To derivatize the compound, graduate student Erick B. Iezzi HTTP://PUBS.ACS.ORG/CEN
treated a few milligrams of it with an isochromanone, a reagent that adds to a fullerene double bond via a [4 + 2] cycloaddition. Dorn's collaborators at the University of California, Davis—Alan L. Balch and Marilyn M. Olmstead—have confirmed the structure of the derivative using singlecrystal X-ray diffraction. That work will be published separately Although the derivative itself is not water soluble, it could easily be made water soluble by replacing its methoxy groups with carboxyl groups, for instance. Chemistry professor Stephen R. Wilson of New York University, a pioneer in exploring the medical applications of fullerenes, calls Dorn's work "extremely exciting" because, by making metallofullerenes water soluble, Dorn has opened the door to using them in the body Radioactive metals can be delivered to tissues in the form of metal chelates, Wilson points out, but the metal can get loose and SCIENCE
wander where it shouldn't. But when the radionuclide is encased in a fullerene, it can't leak out. Dorn's metallofullerene synthesis, in which the trimetallic nitride serves as a template for growing a fullerene shell around the nitride cluster, is "a breakthrough," in Wilson's view, because it allows metal-containing fullerenes to be produced in much higher yields than are otherwise possible. And now that the Virginia Tech group has shown that these metallofullerenes can be functionalized in much the same way as empty fullerenes, Wilson says, it "opens up a newfieldof chemistry" The limited availability of metallofullerenes has hampered efforts to study and apply them, Dorn says. His group is now gearing up to produce hundreds of milligrams of the trimetallic nitride-containing fullerenes. The technology has been licensed to Luna Innovations, a company in Blacksburg that is developing these compounds into MRI contrast agents and other commercial products.—RON
REACTION DU JOUR W+2] cycloaddition yields metallofullerene derivative.
DAGAN I
POLICY
NAS Urges Ban On Reproductive Cloning
H
uman reproductive cloning is dangerous, likely to fail, and should be subject I to a legally enforceable ban, concludes a National Academy of Sciences committee that studied the scientific and medical aspects of human reproductive cloning. "Human reproductive cloning should not now be practiced," said study chairman Irving L Weissman, a professor of cancer biology at Stanford University School of Medicine, at a Jan. 18 news conference in Washington, D.C. Weissman defined human reproductive cloning as the implantation in a woman's uterus of a blastocyst that has undergone nuclear transplantation. He said scientists' experience with five other mammalian species
shows a failure rate that is unacceptable for humans. Many cloned animals die in utero, the panel said, and those that do survive frequently exhibit severe birth defects. However, the panel said nuclear transplantation stem cell research should not be banned. By coincidence, President George W. Bush's newly appointed Council on Bioethics convened its first meeting one day before the NAS study was released. Bush said that he would form such a panel when he announced his policy on stem cell research in August. The 17 members of the bioethics advisory panel are listed at http://www.whitehouse.gov/news/ releases/2002/01/20020116-9.html.—WILLIAM SCHULZ
C&EN
/ JANUARY
28,
2002
15
