Dicyclohexyl carbodiimide cyclization with

A recent report describes the conversion of A-formyl- and N-acetyl-L-leucine into optically active azlactones with dicyclohexyl-carbodiimide (DCC) [Eq. (29)]. Other cyclization reagents, e.g. acetic anhydride, POCI3, SOCI2, and polyphosphoric acid, cause racemiza-tion. These azlactones react with optically active amino acid esters to give esters of dipeptides with retention of activity. 

The initial syntheses of Cypridina luciferin and its analogues were performed in low yields by reaction of appropriate 2-aminopyrazines with a-keto acids, followed by reduction with aluminum amalgam or catalytic hydrogenation, and treatment of the product with dicyclohexyl-carbodiimide. For example, 2-amino-5-phenylpyrazine (36) on reaction with pyruvic acid gave the product 37, which was reduced to give an intermediate formulated as 38, which was then cyclized to give the 0x0 compound 39 in 7% yield. It was later discovered that these products could be obtained in high yield in one step by reaction of aminopyrazines such as 36 with a-keto aldehydes such as pyruvaldehyde (MeCOCHO). Condensation of the appropriate aminopyrazine with... 

Trifluorooxazolidinones are also produced by reacting amino acids with trifluoroacetic anhydride [124-126]. Cyclization was also achieved with 1,3-dicyclohexyl-carbodiimide (DCCI) [127]. The mass spectra of these compounds are also available [128]. 

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