Valine revised

Cyclodidemnamide (60) is a weakly cytotoxic, heptapeptide from D. molle from the Philippines [90]. Total synthesis of the proposed structure of cyclodidemnamide gave a product with different spectral data to those of the natural product, which is thought to be a stereoisomer [91]. The stereochemistry of one of the two valine residues in cyclodidemnamide was revised from L-valine to D-valine as a result of the total synthesis of both isomers [92] and the configuration was also reassigned as a result of total synthesis [93]. The hexapeptides, comoramides A (61) and B (62), were isolated from D. molle from Mayotte lagoon in the Comoros Islands, while the heptapeptides, mayotamides A (63) and B (64) were isolated from a separate collection of D. molle from the Comoros Islands [94]. 

CRC Handbook should be revised downward by 0.4 (glycine), 2.0 (phenylalanine), and 4.8 (valine) kcal/mol. Our best theoretical values are in good agreement with the recently reported experimental values of Roux and coworkers for alanine [15] and methionine, [18] but suggest that their experimental value for cysteine should be revised downward by 2.8 kcal/mol. Finally, our best theoretical values for alanine and glycine are in excellent agreement with the recent values of Dorofeeva and Ryzh-ova [97]. 

Esperinic acid was studied by mass spectrometry and the revised structure (42) was established (705), in which 30% of the C-terminal l-leucine was replaced by L-valine. In order to locate the lactone ring esperin was treated with hydrazine followed by Curtius rearrangement... 

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