Structurally Diverse Duclauxins from a Coral-Derived Talaromyces sp. and Insight into Determining the Configuration at C-1 of Heptacyclic Duclauxins by 1 H NMR

A chemical investigation of the coral-derived fungus sp. TJ403-AL05 led to the isolation of 18 duclauxin analogues ( - ), 14 of which, taladuxins A-N ( - ), are new and consist of the first example of duclauxin fused with one 1,6-dioxaspiro[4.5]decan-2-one moiety ( ), as well as its biosynthetic product ( ), and 12 6/6/6/5/6/6/6 heptacyclic derivatives ( - ). Comprehensive spectroscopic analyses, electronic circular dichroism (ECD) calculations, DP4+ probability analyses, single-crystal X-ray diffraction, and vibrational circular dichroism (VCD) calculations were employed to characterize their structures and revise the published structure of verruculosin B. An efficient H NMR method was established to discriminate 1 and 1 configurations at C-1 of 6/6/6/5/6/6/6 heptacyclic duclauxins according to chemical shift differences of diastereotopic methylene H -11 or H -12 (Δδ or Δδ ). Compounds , - , - , and exhibited moderate inhibition of 4-hydroxyphenylpyruvate dioxygenase ( HPPD), with IC values ranging from 17.1 to 71.3 μM.