Abstract
Nostosins A and B were isolated from a hydrophilic extract of Nostoc sp. strain from Iran, which exhibits excellent trypsin inhibitory activity. Nostosin A was the most potent natural tripeptide aldehyde as trypsin inhibitor up to now. Both r- and s-2-hydroxy-4-(4-hydroxy-phenyl)butanoic acid (Hhpba) were prepared and incorporated into the total synthesis of nostosin B, respectively. Careful comparison of the NMR spectra and optical rotation data of synthetic nostosin B (1a and 1b) with the natural product led to the unambiguous identification of the r-configuration of the Hhpba fragment, which was further confirmed by co-injection with the authentic sample on HPLC using both reversed phase column and the chiral AD-RH column.
Highlights
Nostosin A and B were isolated from a hydrophilic extract of Nostoc sp. strain obtained from a paddy field in Iran (Figure 1) [1]
Nostosins A and B are distinctive trypsin inhibitors isolated from nature, the C‐2
B are distinctive trypsin inhibitors isolated from nature,development theofC-2 stereochemistry
Summary
Nostosin A and B were isolated from a hydrophilic extract of Nostoc sp. strain obtained from a paddy field in Iran (Figure 1) [1]. Aand B could be classified as natural small linear peptides that act as trypsin inhibitors [2,3,4,5] These small peptides structurally feature an arginine motif at the C-terminal, which has been proven to be crucial for their interactions with the protease targets [6,7,8,9,10,11]. Nostosin A was more potent than the commercially available trypsin inhibitor leupeptin (IC50 = 0.5 μM), rendering it as the most potent tripeptide natural trypsin inhibitor up to now Both nostosin A and B contain three subunits, 2-hydroxy-4-(4-hydroxyphenyl)butanoic acid (Hhpba), L-Ile and L-Arg, the C-terminal of nostosin B exists as the reduced form of nostosin A, which dramatically diminished its biological activity (158-fold compared to nostosin A), similar to aeruginosin
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