[D-Leu1] microcystin-LR, a new microcystin isolated from waterbloom in a Canadian prairie lake

A previously undescribed cyclic heptapeptide hepatotoxin was isolated from a cyanobacteria waterbloom collected in Pakowki Lake, Alberta, Canada (49 degrees 20'N and 110 degrees 55'W). The compound was characterized by amino acid analysis, ESIMS/CID/MS, H-1 and C-13 NMR, and UV spectroscopy. Structure of the new microcystin was assigned as [D-Leu(1)] microcystin-LR (1). The amino acid composition is the same as microcystin-LR (2) except for D-Leu and L-Leu in 1 instead of D-Ala and L-Leu in 2. This is the first microcystin identified, among the 64 known microcystins, that has both a D- and L-Leu amino acid. Toxicity as measured by the protein phosphatase inhibition activity of 1 is similar to microcystin-LR. The presence of microcystins in waterblooms from this lake is discussed in relation to the almost yearly bird mortalities that have occurred there since 1995. (C) 2001 Elsevier Science Ltd. All rights reserved.