Chiral2-sulfonyloxaziridines, 9-12, afford the best enantioselectivity of any chiral oxidizing reagent for the asymmetric oxidation of sulfides and disulfides to sulfoxides and thiosulfinates, respectively, 5-8 times better than chiral peracids. For asymmetric oxidations using 9-12, the configuration of the oxaziridine three-membered ring was shown to control the configuration of the product, which could be predicted using a chiral recognition mechanism (Figure 2). The increased asymmetric bias exhibited by chiral 2-sulfonyloxaziridines was attributed to the fact that the active-site oxygen was incorporated into a rigid chiral environment. The group size difference (GSD) effect in both the oxaziridine and substrate play important roles in determining the absolute configuration of the product and the magnitude of the asymmetric bias. As the GSD increases the enantioselectivity increases.

J. Am. Chem. SOC this would lead to A(AG*N) = 3.4 kcal/mol, because we already decided A(AG*,) for 2 was about 0.5. This gives AG" for 2(Me) of 7.1-3.4 = 3.7 kcal/mol. This number is not unreasonable. Assuming proportionally of AG" for chloramines and methylamines seems to work as far as it can be tested. For 3(Me) assuming proportionality gives AG'N = 5.3; the number from N M R measurement is 5.5 kcal/mol. A similar estimate for 2(Me) Abstract: Diastereomeric 2-sulfonyloxaziridines (-)-(S,S)-l and (+)-(R,R)-2 epoxidize unfunctionalized olefins 3a-g, affording epoxides 4a-g with better enantioselectivity than do chiral peracids or hydroperoxides. The configuration of the oxaziridine three-membered ring controls the stereochemistry of the product. The mechanism of chiral recognition is largely determined by steric factors where the orientations of the oxaziridine three-membered ring and the alkene are planar in the transition state.The fundamental factors that control asymmetric induction remain unclear despite impressive recent achievements in the asymmetric formation of C-C and C-H This is particularly true for the asymmetric oxidation of unfunctionalized 0002-7863/83/1505-3123$01.50/0 0 Abstract: The *-facial stereoselectivities exhibited by cyclopentadienide anions 3 and 4 in their reactions with methyl iodide, three geminally dideuterated 1,2-disubstituted ethanes, epichlorohydrin, C1(CH2)$D21, 1,4-dibromo-2-isopropylidenebutane, and deuterium oxide were determined. Analysis was achieved by a combination of 'H and 2H NMR spectroscopy, Diels-Alder

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The effects of polyamines on the loss of biological activity of bacterial transforming DNA irradiated in the absence and presence of sulphydryl-containing compounds has been investigated. In both oxygenated and hypoxic conditions the polyamines (spermine, spermidine, putrescine and cadaverine) are radioprotectors with the degree of protection increasing with increasing polyamine concentration. When O2-saturated DNA solutions are irradiated, the degree of radioprotection by polyamines generally correlates with the efficiency of scavenging of OH. radicals. In N2 the protection does not show that correlation; several possible reasons are discussed. With the exception of spermine, the polyamines are slightly more protective of oxygenated DNA than of hypoxic DNA. When DNA is irradiated in the presence of both polyamines and thiols, the combined protection is usually greater than that exhibited by either agent alone. When irradiation is in oxygen, the combined agents appear to operate by the same mechanism, namely OH. radical scavenging. In N2-saturated solutions, polyamines and dithiothreitol appear to act by different, non-interacting mechanisms; however WR1065 and polyamines may radioprotect by the same mechanism. Also, the results suggest that polyamines may reduce the ability of some thiols to radioprotect DNA.