Total Synthesis of (+)-Lactacystin

A concise enantioselective entry to the synthesis of deoxy-azasugars

[reaction: see text] A concise enantioselective preparation of oxazolidinylpiperidine 4, a key intermediate in the synthesis of glycosidase inhibitors such as 1-deoxymannojirimycin or 1-deoxygalactostatin, has been developed. Sharpless catalytic asymmetric epoxidation of (E)-2,4-pentadienol followed by treatment with allyl isocyanate afforded epoxy carbamate 8. Regioselective intramolecular ring opening promoted by sodium bis(trimethylsilyl)amide and ring-closing metathesis provided the bicyclic intermediate 4 in high enantiomeric purity. The four-step sequence takes place in 51% overall yield.

Reversal of regioselection in the sharpless asymmetric aminohydroxylation of aryl ester substrates

[formula: see text] The asymmetric synthesis of beta-hydroxy-alpha-amino acids is reported which relies on the use of alpha,beta-unsaturated aryl ester substrates and the dihydroquinyl alkaloid ligand system (DHQ)2-AQN to control the regio- and enantioselectivity of the asymmetric aminohydroxylation (AA) process. alpha,beta-Unsaturated ester substrates of type 1 have a significant effect on the substrate-ligand recognition event which results in a reversal of regioselectivity in the AA reaction.

Diastereoselective Synthesis of alpha,alpha-Disubstituted gamma-Carboxypyroglutamates via Sm(III)-Azomethine Ylide Cycloadditions

Sm(III)-azomethine ylides 2 have been generated from ketones 1. Cycloaddition of ylides 2 with alpha,beta-unsaturated esters 3 through a transition state chelation-controlled by the metal allowed for the asymmetric synthesis of gamma-carboxypyroglutamates having a quaternary alpha-carbon that are potentially useful in the synthesis of neuroprotective agents.

The design and synthesis of 2,5-linked pyrrolinones. A potential non-peptide peptidomimetic scaffold

The de novo design and initial synthetic studies directed toward construction of a novel non-peptide scaffold for beta-strand/sheet and related secondary peptide structural mimics are described. The scaffold, consisting of a repeating array of 2,5,5-trisubstituted pyrrolinone (enaminone) units punctuated with appropriate amino acid side chains, is conceptually related to our previously successful 3,5-linked polypyrrolinone non-peptide peptidomimetic scaffold. Construction of the 2,5,5-trisubstituted pyrrolinone ring system proceeds via intramolecular condensation of an N-protected amino dione. The latter is prepared from a protected alpha-amino ketone and aldehyde via an aldol-oxidation reaction sequence.