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Chemical analysis reveals new putative ecteinascidin precursors in the Caribbean tunicate Ecteinascidia turbinata, highlighting their unique cysteine unit stereochemistry.
New bioactive ecteinascidins (Et's) 597 ( 1 ), 583 ( 2 ), 594 ( 3 ), and 596 ( 4 ) putative biosynthetic precursors of previously described Et's [e.g., Et 743 ( 5 )] were isolated from the Caribbean tunicate Ecteinascidia turbinata . Structures assigned to these compounds based on spectroscopic data represent a novel series of Et's with l -cysteine or its α-oxo analog as unit C. The absolute configuration of the l -Cys unit of 1 was assigned by chiral GC, while a 2D ROESY (rotating-frame Overhauser enhancement spectroscopy) spectrum of its acetyl derivative 1a completed the assignment of the stereochemistry of 1 as 1 R,2 R,3 R,4 R,11 R,13 S,21 S,1‘ R .
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Sakai et al. (1996) studied this question.
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