Synthesis of the oxazolidinone fragment of thelepamide

Thelepamide, an unique ketide-amino acid isolated from a marine annelid worm Thelepus crispus, has a unique oxazolidinone ring derived from cysteine, glycine and valine. Rareness in nature as well as promising bioactive possibility make the oxazolidinone ring an attractive synthetic target. The hydroxy oxazolidinone fragment of thelepamide was prepared by acid-catalysed N,O-acetal formation between a ketoamide and formaldehyde. Lactone-carbonyl selective isopropyl addition to an oxazilidine-dione under Grignard conditions also forms the target compound.

An expeditious synthesis of the ascomycete metabolite rigidiusculamide B

l-Tyrosine is converted diastereoselectively to (−)-rigidiusculamide B via a Li₂Te-triggered cyclisation followed by a desilylation–oxidation of the resulting tetramate.

Thelepamide: an unprecedented ketide-amino acid from Thelepus crispus, a marine annelid worm

Thelepamide (1) was characterized during a program to study cytotoxic substances from an unusual source, the tidal zone-derived annelid Thelephus crispus. Its structure contains a tetraketide and a tripeptide subunit and possesses striking atom diversity, consisting of 17 carbons and 8 heteroatoms. The relative configurations at four chiral sites were elucidated via ROESY, J-based configurational analysis, and DFT calculations. It was modestly active against leukemia cells (IC50 = 5 μg/mL) and inactive against solid tumor cell lines.