lithium-bis(trimethylsilyl)amide and hexamethylsilazane

Polypeptides have broad applications and can be prepared via ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Conventional initiators, such as primary amines, give slow NCA polymerization, which requires multiple days to reach completion and can result in substantial side reactions, especially for very reactive NCAs. Moreover, current NCA polymerizations are very sensitive to moisture and must typically be conducted in a glove box. Here we show that lithium hexamethyldisilazide (LiHMDS) initiates an extremely rapid NCA polymerization process that is completed within minutes or hours and can be conducted in an open vessel. Polypeptides with variable chain length (DP = 20-1294) and narrow molecular weight distribution (Mw/Mn = 1.08-1.28) were readily prepared with this approach. Mechanistic studies support an anionic ring opening polymerization mechanism. This living NCA polymerization method allowed rapid synthesis of polypeptide libraries for high-throughput functional screening.

Topics: Amines; Amino Acids; Anhydrides; Anti-Bacterial Agents; Drug Resistance, Multiple, Bacterial; Lithium Compounds; Methicillin-Resistant Staphylococcus aureus; Organosilicon Compounds; Peptides; Polymerization; Pseudomonas aeruginosa; Silanes

'Conventional' (-)-sparteine adducts of lithium and sodium 1,1,1,3,3,3-hexamethyldisilazide (HMDS) were prepared and characterised, along with an unexpected and 'unconventional' hydroxyl-incorporated sodium sodiate, [(-)-sparteine x Na(mu-HMDS)Na x (-)-sparteine](+)[Na(4)(mu-HMDS)(4)(OH)](-)--the complex anion of which is the first inverse crown ether anion.

Topics: Crystallography, X-Ray; Lithium Compounds; Metals, Alkali; Molecular Conformation; Organosilicon Compounds; Silanes; Sparteine