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A new method for the protection of primary amines or amino alcohols as phthalimides is described. The phthaloyl group is selectively introduced under mild, anhydrous conditions by reacting the amine with 2-(ethoxycarbonyl)benzoic acid activated by PyBOP, followed by the thermally induced cyclization of the resulting phthalamic ester. These reaction conditions are applicable to a variety of primary amines and good yields are obtained in all cases.

A catalytic asymmetric synthesis of N-phthaloyl (S)-γ-[(S)-1-aminoalkyl]-γ-lactones, widely used intermediates in the preparation of hydroxyethylene dipeptide isosteres, is described. The highly enantiopure epoxy alcohols arising from the Sharpless epoxidation of (E)-allyl alcohols are first converted to (S)-N-phthaloyl-[(S)-1-aminoalkyl]oxiranes by means of an efficient four-step sequence involving the regio- and stereoselective ring opening of the starting epoxide by azide, reduction, phthaloylation, and intramolecular Mitsunobu cyclization of the intermediate phthalimido diol. Treatment of the resulting oxirane with lithium (1R)-menthyloxyacetylide in the presence of boron trifluoride etherate, followed by in situ hydrolysis of the ynol ether, leads to a (4R,5S)-5-phthalimido-4-hydroxy ester. A Mitsunobu reaction with p-nitrobenzoic acid (which establishes the correct (S)-configuration at C-4) and subsequent selective saponification of the benzoate and cyclization of the inverted hydroxy ester afford the target N-protected (S)-γ-[(S)-1-aminoalkyl]-γ-lactones. Using this methodology, lactones 19 and 26 were obtained in seven steps from the readily available epoxy alcohols 5 and 20, respectively, in high enantiomeric purity.

The natural dipeptide antibiotic TAN 1057 A,B represents a promising new antibiotic entity. In this communication we report a novel approach for the synthesis of TAN 1057 A,B analogs bearing variations in the β-arginine side chain. This approach involves a combination of liquid and solid phase methods and allows for a library synthesis of analogs of the natural product.