title: Concise total synthesis of the thiazolyl peptide antibiotic GE2270 A.
abstract: The potent antibiotic thiazolylpeptide GE2270 A was synthesized starting from N-tert-butyloxycarbonyl protected valine in a longest linear sequence of 20 steps and with an overall yield of 4.8 %. Key strategy was the assembly of the 2,3,6-trisubstituted pyridine core by consecutive cross-coupling reactions starting from 2,6-dibromo-3-iodopyridine. The complete Southern fragment was installed by Negishi cross-coupling of 3-zincated 2,6-dibromopyridine at the terminal 2-iodothiazole of a trithiazole (87 %). The substituent at C-6 representing the Northern part of the molecule was introduced in form of the truncated tert-butyl 2-bromothiazole-4-carboxylate after metalation to a zinc reagent by another Negishi cross-coupling (48 %). Decisive step of the whole sequence was the macrocyclization to a 29-membered macrolactam, which was conducted as an intramolecular Stille cross-coupling occurring at C-2 of the pyridine core and providing the desired product in 75 % yield. The required stannane was obtained by amide bond formation (87 %) between a complex dithiazole fragment representing the Eastern part of GE2270 A and a 3,6-disubstituted 2-bromopyridine. Final steps included attachment of a serine-proline amide dipeptide to the Northern part of the molecule (65 %), formation of the oxazoline ring and silyl ether deprotection (55 % overall).
authors.affiliation: Lehrstuhl für Organische Chemie 1, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany.
authors.forename: Oscar
authors.initials: O
authors.lastname: Delgado
authors.forename: H Martin
authors.initials: HM
authors.lastname: Müller
authors.forename: Thorsten
authors.initials: T
authors.lastname: Bach
mesh_terms: D000577:Amides / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D007769:Lactams / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D013844:Thiazoles / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000577:Amides; D000900:Anti-Bacterial Agents; D003432:Cross-Linking Reagents; D007769:Lactams; D010456:Peptides, Cyclic; D011725:Pyridines; D013844:Thiazoles; C068122:GE 2270 A