1. Diastereoselective Synthesis of 1-Deoxygalactonojirimycin, 1-Deoxyaltronojirimycin, and N-Boc-(2S,3S)-3-Hydroxypipecolic Acid via Proline Catalyzed α-Aminoxylation of Aldehydes
Shibin Chacko, Ramesh Ramapanicker J Org Chem. 2015 May 1;80(9):4776-82. doi: 10.1021/acs.joc.5b00424. Epub 2015 Apr 17.
An efficient synthesis of deoxygalactonojirimycin and deoxyaltronojirimycin through the use of proline catalyzed asymmetric α-aminoxylation of a higher homologue of Garner's aldehyde, derived from l-aspartic acid, is reported. The method is also used for a highly diastereoselective synthesis of the N-Boc derivative of (2S,3S)-3-hydroxypipecolic acid. The configuration of the proline catalyst used for the asymmetric aminoxylation step ultimately controls the absolute configuration of three adjacent stereogenic centers in the final products.
2. Preparation of Aminoalkyl Chlorohydrin Hydrochlorides: Key Building Blocks for Hydroxyethylamine-Based HIV Protease Inhibitors
Pierre L. Beaulieu, Dominik Wernic J Org Chem. 1996 May 31;61(11):3635-3645. doi: 10.1021/jo960109i.
Enantiomerically pure N,N-dibenzyl-alpha-amino aldehydes reacted with (chloromethyl)lithium, generated in situ from bromochloromethane and lithium metal, to give predominantly erythro aminoalkyl epoxides. Treatment of the crude epoxides with aqueous hydrochloric acid gave crystalline (2S,3S)-N,N-dibenzylamino chlorohydrin hydrochlorides in 32-56% overall yield and high isomeric purity. These compounds are versatile synthetic intermediates for the preparation of hydroxyethylamine-based HIV protease inhibitors, either directly as such, or via conversion to the corresponding N-Boc-(2S,3S)-aminoalkyl epoxides. The processes described do not make use of hazardous reagents or intermediates, do not require chromatographic purifications, and are thus amenable to the preparation of large quantities of these versatile building blocks.
3. Synthesis of N-Fmoc-(2S,3S,4R)-3,4-dimethylglutamine: An application of lanthanide-catalyzed transamidation
Selçuk Calimsiz, Mark A Lipton J Org Chem. 2005 Aug 5;70(16):6218-21. doi: 10.1021/jo050518r.
N-Fmoc-(2S,3S,4R)-3,4-dimethylglutamine (6) was synthesized from tert-butyl N-Boc-(2S,3S,4R)-dimethylpyroglutamate (13). This synthesis involved selective deprotection of a Boc group from a lactam nitrogen in the presence of a tert-butyl ester, Fmoc protection of the lactam, and a lanthanide-catalyzed transamidation reaction of the Fmoc-protected lactam, using ammonia and dimethylaluminum chloride. The scope of Lewis acid-catalyzed transamidation of acylated lactams was explored through the variation of lanthanide, lactam, acyl group, amine, and aluminum reagent. The reactivity of various metal triflates was found to vary in the following qualitative order: Yb approximately Sc > Er approximately Eu approximately Sm > Ce approximately Ag(I) > Cu(II) approximately Zn. Intriguingly, catalysis was only observed when ammonia was the nitrogen nucleophile; addition of other amidoaluminum complexes to acyl lactams was found to be insensitive to the addition of lanthanides.
