Total syntheses of the thiopeptides amythiamicin C and D.
The thiopeptides amythiamicin C and D were synthesized by employing amide bond formation, a Stille cross-coupling reaction, and two Negishi cross-coupling reactions as key transformations. The central 2,3,6-trisubstituted pyridine ring of the target compounds was introduced as a 2,6-dibromo-3-iodopyridine, which was selectively metalated at the 3-position and connected to the complete Southern fragment of the amythiamicins by a Negishi cross-coupling. For the synthesis of amythiamicin C, this step was followed by a Negishi cross-coupling at C-6 of the pyridine core. Subsequent attachment of the Eastern fragment was achieved by amide bond formation and macrolactam ring closure by a Stille cross-coupling at C-2. The Eastern bithiazole fragment of the amythiamins was constructed also by regioselective metalation and cross-coupling reactions. The pivotal step involved the diastereoselective addition of 4-bromothiazole-2-magnesium bromide to a chiral sulfinyl imine. For the synthesis of amythiamicin D, the order of cross-coupling at C-6, amide bond formation, and cross-coupling at C-2 was changed. The amide bond formation to the Eastern fragment was performed first and it was subsequently attempted to close the macrolactam by an intramolecular regioselective Stille cross-coupling at C-2. Despite the low regioselectivity of this reaction it paved the way to the immediate completion of the amythiamicin D synthesis when followed by a Negishi cross-coupling at C-6 with 2-zincated methyl thiazole-5-carboxylate.
Lehrstuhl für Organische Chemie I, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany.
Carolin
C
Ammer
Thorsten
T
Bach
D000577:Amides / Q000737:chemistry*; D000603:Amino Acids, Sulfur / Q000138:chemical synthesis* / Q000737:chemistry; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D013844:Thiazoles / Q000138:chemical synthesis* / Q000737:chemistry
D000577:Amides; D000603:Amino Acids, Sulfur; D047028:Macrocyclic Compounds; D013844:Thiazoles; C088501:amythiamicin D; C088500:amythiamicin C