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a) Diastereomer library screened for N-methylation selectivity. Arrows represent sequences that showed >95% selectivity for a single partially methylated species; all other sequences showed no reaction, permethylation, or mixtures of N-methyl products of varying complexity. Scaffolds 18 and 19 correspond to compounds 2 and 1, respectively. b) Consensus sequences for trimethyl- and tetramethyl-selective compounds.
