The streptogramin A antibiotics have proven to be highly active against Gram positive bacteria, particularly methicillin-resistant Staphylococcus aureus. Members of this group of compounds are characterized by a 23-membered macrocycles containing polyene, oxazole, amide and ester functionality. The chemistry and biology of these valuable antimicrobial agents is covered.
Methodology for preparation of the C8-C16 dienylamine segment of the streptogramin antibiotics is based on a diastereoselective nitrile oxide-olefin cycloaddition to a (triene)iron complex. The Fe(CO)3 adjunct also serves as a protecting group for the subsequent reductive hydrolysis of the isoxazoline ring
To a mixture of 2-cinnamyl-1,3-oxazole-4-carboxaldehyde [1,2] (2.8 g, 14 mmol) and ethanedithiol (2.3 g, 21 mmol) in methylene chloride (100 ml) was added boron trifluoride etherate (2.8 g, 21 mmol). The reaction mixture was stirred overnight at room temperature. The reaction mixture was washed with aqueous sodium hydroxide (5%, 50 ml), and aqueous phase was extracted with ether. The combined organic layers were dried (MgSO 4 ), and concentrated. The residue was purified by column chromatography (SiO 2 , 3:1 hexanes/ethyl acetate) to give 2-(2'-cinnamyl-1',3'-oxazolyl)-1,3-dithiolane as a light yellow solid (2.25 g, 66%).
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