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4-Chloro-2-tribromomethylquinoline (1) showed unexpected, albeit low, antimalarial activity. Structural variation (Table I) revealed that the activity was Table I Activities of Some 2-Tribromomethylqcinolines and Other Active Halogen Compounds" Dose, AMST,6 No. Ra R4 r5 Rs mg/kg days lc CBra Cl H H 40

The progress of the rearrangement could be followed easily by the shift of the carbonyl absorption in the infrared spectrum from the thiol ester position (5.95 p in the case of the acetate esters) to the amide position a t about 6.15 p . I n most cases the amide was isolated by direct distillation, the polythioformaldehyde remaining undistilled, m.p. 185-190".L6 The infrared and n.m.r. spectra of the latter were identical with those of an authentic sample.In the presence of base, a typical thiolsulfonate reacts readily and completely with a thiol to form a disulfide and a sulfinic acid salt even a t -86". In the absence of base, fairly rapid reaction occurs, which proceeds only part way, but can be pushed toward completion by use of excess thiol or thiolsulfonate. Steric factors significantly affect reactivity of thiolsulfonates, more so than do electronic effects noted thus far. As ancillary points, gas-liquid chromatography was investigated for qualitative and quantitative analysis of thiols, and a tertiary alkyl thiolsulfonate was synthesized, apparently for the first time.(1) (a) This investigation was supported by the U. S.

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The resolution and sensitivity of electron paramagnetic resonance (EPR) and saturation transfer EPR (ST-EPR) for biological applications are greatly improved by deuteration and substitution of 15N for 14N in the spin-labeled probe N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide (MSL We have shown that the sensitivity and resolution of electron paramagnetic resonance (EPR) and saturation transfer EPR (ST-EPR) spectroscopy were substantially improved for biological studies by deuteration of the frequently used maleimide spin label N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide (MSL) which binds covalently to proteins (1, 2). Significant gains in detectability and resolution were observed with [2H]MSL in both the fast motion limit for freely tumbling spin label (rc 10 psec) and in the slow to very slow correlation time range exhibited by labeled proteins such as bovine serum albumin and hemoglobin in viscous media (0.1 ,usec s rT ' 1 msec). The improvements resulted from a reduction in the inhomogeneous line broadening due to the weaker superhyperfine interactions of the unpaired electron with deuterium than with hydrogen.To further advance our capabilities for interpretation of spectra of labeled proteins, we prepared the doubly substituted that 15N or deuterium substitution increased sensitivity for a freely tumbling spin label and that '5N simplified the spectrum by reduction of the number of nuclear manifolds from three to two (4-9). However, a doubly substituted probe with '5N and deuterium had not been prepared previously. The potential increase in sensitivity and resolution of such a probe seemed particularly advantageous in biological systems in which the substances to be spin labeled are often present in low concentrations and are macromolecules with slow correlation times in the range appropriate for analysis by ST-EPR techniques. (11,12) and spin labeled with a given maleimide analogue at a ratio of one spin label per tetramer as described by Beth et al. (13). GAPDHase activity was 28% inhibited by MSL and its two analogues.

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