surface modifications. Such a relationship exists between the Jovian moons Io and Europa, with the result being that Io remains volcanically active. As Voyager 2 departed from Saturn, it also photographed the most far-flung Saturnian moon, Pheobe, which orbits almost 13 million km from the planet. And again, there were surprises. Phoebe's orbit, known from Earth-based observations, is retrograde—it orbits Saturn in the direction opposite that of the other moons and the rings. This has led scientists to speculate that it is not a natural moon of Saturn, but rather a captured asteroid or fragment. However, according to Soderblom, it does not look like a fragment. It is spherical, suggesting that it is a primitive accretionary body. Also, Soderblom says, its dark composition suggests some similarity to the other, outer
Saturnian moons. At this point, Pheobe's origin remains a matter of speculation. Of course, Voyager 2 also looked closely at Saturn itself. According to imaging team leader Smith, images of Saturn appear crisper than in Voyager 1 photographs. Scientists at one time thought that much of the lack of variegated color on Saturn compared to Jupiter was due to haze obscuring the cloud tops, but the evidence from Voyager 2 suggests that this is not the case. Apparently, Smith says, the chromophores in Saturn's clouds are simply better mixed than on Jupiter. But a number of features do show up. Saturn has a pattern of jet streams that extend to much higher northern latitudes than on Jupiter. Vorticity, cyclonic and anticyclonic, clearly exists in the troughs of an undulating jet stream in Saturn's mid-northern latitudes. Some rela-
New analgesic more potent than morphine
Pfizer currently is engaged in extensive clinical trials with oral and injectable forms of levonantradol, according to Johnson. Its early use has been in controlling nausea in cancer patients who do not respond to other available drugs. However, the drug also is being tested for controlling pain. In animals, the drug appears to be from nine to 30 times more potent than morphine, according to Johnson. Perhaps more important, the drug might not induce physical dependence (addiction) in users, and also might not induce tolerance. Many opiates, including morphine, must be administered in increasing doses to achieve the same level of effect because a user grows "tolerant" of the drug. Although levonantradol has many of morphine's analgesic properties, the two drugs seem to act differently. For instance, levonantradol does not bind to morphine receptor molecules in vitro. Also, levonantradol's effects are not reversed by naloxone, a chemical that acts as an antagonist to many members of the opiate family. Levonantradol "neither acts directly at nor indirectly through the opiate receptor," the Pfizer group says. The researchers speculate that levonantradol and other similar compounds "act stereospecifically at a novel, and as yet unidentified, receptor." One unusual way in which levonantradol might exert activity in the body is by affecting prostaglandins, Johnson says. He and his colleagues have examined space-filling models
Hashish has problems, any serious student of its potential clinical uses will tell you. Thus it comes as no surprise that medicinal chemists have sought to refine this time-honored analgesic, wishing to transform its promising natural endowment into a richer, more useful drug for the clinic. Speaking at the 182nd American Chemical Society national meeting in New York City recently, M. Ross Johnson of Pfizer central research, Groton, Conn., described a program begun in 1975 to design a molecule based on the active ingredients of Cannabis satavia, the marijuana plant, that "would incorporate structural features necessary for analgesia." He also described recent work suggesting that some new analgesics could interfere with prostaglandin metabolism in the body. The best candiate the Pfizer group has found so far is levonantradol, a specific stereoisomer of nantradol, "a structurally novel phenanthridine analgesic that possesses two to seven times greater potency than morphine," according to Johnson and his colleague George M. Milne. The Pfizer group says that levonantradol is about 100-fold more active than its dextrorotatory isomer. Originally, nantradol was made as an equal mixture of the two stereoisomers, but now levonantradol can be obtained separately.
tively permanent features exist. A brown spot, reminiscent of Jupiter's great red spot, was seen by both Voyagers at 74° north latitude. Though much smaller than the great red spot, the anticyclonic feature is still impressive in size. It measures 10,000 km by 6000 km. Much of the data from other Voyager instruments that were focused on Saturn are still being analyzed. Studies with the photopolarimeter will yield information on the particle size distribution in the upper atmosphere. Measurements using the infrared interferometer spectrometer will augment Voyager 1 data on temperature variations in the clouds. Measurements with the ultraviolet spectrometer will help determine atmospheric constituents. And Saturn's complex magnetosphere, which contains an unexplained longitudinal asymmetry, was explored with a number of Voyager 2 instruments. D
Levonantradol: cannabinoid-derived analgesic
of the drug and of prostaglandin E2, one of several 20-carbon-containing fatty acids found in the body. Prostaglandins are highly potent molecules involved in mediating many activities, such as responses like nausea and diarrhea and reactions to injury. When the Pfizer chemists compared key interatomic angles and distances in models of the two compounds, they "observed striking conformational similarities." Such similarities might help explain how levonantradol acts in the body. "Unlike morphine, both prostaglandin E 2 and levonantradol are nearly planar molecules," Johnson says. "Both have the two key hydroxyls in the same absolute configuration and are coupled to a lipohilic tail . . . . Levonantradol might exert some of its effects by interfering with prostaglandin functions." Recent direct evidence adds further support to that idea, Johnson says. Researchers now find that levonantradol can block prostaglandin-induced diarrhea in animals. D Sept. 21, 1981 C&EN
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