| Summary: | Application of a miniaturized 24-well plate system for cultivation profiling (MATRIX) permitted optimization of the cultivation conditions for the marine-derived fungus <i>Talaromyces</i> sp. CMB-TU011, facilitating access to the rare cycloheptapeptide talarolide A (<b>1</b>) along with three new analogues, B–D (<b>2</b>–<b>4</b>). Detailed spectroscopic analysis supported by Marfey’s analysis methodology was refined to resolve <i>N</i>-Me-<span style="font-variant: small-caps;">l</span>-Ala from <i>N</i>-Me-<span style="font-variant: small-caps;">d</span>-Ala, <span style="font-variant: small-caps;">l</span>-<i>allo</i>-Ile from <span style="font-variant: small-caps;">l</span>-Ile and <span style="font-variant: small-caps;">l</span>-Leu, and partial and total syntheses of <b>2</b>, and permitted unambiguous assignment of structures for <b>1</b> (revised) and <b>2</b>–<b>4</b>. Consideration of diagnostic ROESY correlations for the hydroxamates <b>1</b> and <b>3</b>–<b>4</b>, and a calculated solution structure for <b>1</b>, revealed how cross-ring H-bonding to the hydroxamate moiety influences (defines/stabilizes) the cyclic peptide conformation. Such knowledge draws attention to the prospect that hydroxamates may be used as molecular bridges to access new cyclic peptide conformations, offering the prospect of new biological properties, including enhanced oral bioavailability.
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