Richard H. Mueller

Synthesis of l-β-hydroxyvaline from α-keto-β-hydroxyisovalerate using leucine dehydrogenase from Bacillus species☆

Abstract α-Keto-β-bromoisovaleric acid or its ethyl ester was hydrolyzed with sodium hydroxide to α-keto-β-hydroxyisovalerate and converted in situ to l -β-hydroxyvaline by reaction with NADH and NH3 catalyzed by leucine dehydrogenase from Bacillus species. Methyl 2-chloro-3,3-dimethyloxiranecarboxylate and the corresponding isopropyl or 1,1-dimethylethyl esters were prepared by Darzens condensation. These glycidic esters, after hydrolysis by sodium bicarbonate and sodium hydroxide to α-keto-β-hydroxyisovalerate, were also converted to l -β-hydroxyvaline by leucine dehydrogenase. NAD was recycled to NADH with either formate dehydrogenase from Candida boidinii or glucose dehydrogenase from Bacillus megaterium. Polyethylene glycol-NADH was an effective reductant with formate dehydrogenase and dextran-NAD was effective with glucose dehydrogenase. Reductive amination activity for α-keto-β-hydroxyisovalerate was found in most Bacillus strains screened, including megaterium, subtilis, cereus, pumilus, licheniformis, thuringiensis, and brevis. Highest specific activity was found in B. sphaericus ATCC 4525. pH 8.5 was optimum for both glucose dehydrogenase and reductive amination of α-keto-β-hydroxyisovalerate by the B. sphaericus enzyme. The apparent Km for α-keto-β-hydroxyisovalerate was 11.5 m m compared to 1.06 m m for α-ketoisovalerate. The apparent Vmax with α-keto-β-hydroxyisovalerate was 41% of the value with α-ketoisovalerate, making the enzyme very suitable for the preparation of l -β-hydroxyvaline.

Stereospecific friedel-crafts alkylation of benzene with 4-mesyloxy-L-prolines. A new synthesis of 4-phenylprolines

Abstract The reaction of benzene with cis - and trans -N-benzoyl-4-mesyloxy-L-proline ( 11 and 12 ) in the presence of AlCl 3 stereospecifically produces the corresponding trans - and cis -4-phenylproline derivatives.

β-Lactam synthesis: Cyclization versus 1,2-acyl migration-cyclization. The mechanism of the 1,2-acyl migration-cyclization

Abstract The cyclization of hydroxamate 1 unexpectedly afforded two isomeric β-lactams 2 and 3 . The mechanism for the formation of 3 has been shown by carbon-13 labeling to involve a novel 1,2-acyl migration-cyclization process.

β-Lactam synthesis: chemospecific sulfonation and cyclization of the β-hydroxyvaline nucleus

Abstract The intramolecular cyclization of “hydroxamate” 3 using Mitsunobu conditions was inefficient for the formation and isolation of the C-4 dimethyl monobactam 4 . However, chemospecific O-sulfonation of 1 and subsequent cyclization with base provides a useful method for β-lactam synthesis from a sterically hindered β-hydroxy amino acid. Competitive rearrangement of 3 also occurs during cyclization providing isomeric β-lactam 5 .