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

A chemical investigation of the coral-derived fungus <i>Talaromyces</i> sp. TJ403-AL05 led to the isolation of 18 duclauxin analogues (<b>1</b>-<b>18</b>), 14 of which, taladuxins A-N (<b>1</b>-<b>14</b>), are new and consist of the first example of duclauxin fused with one 1,6-dioxaspiro[4.5]decan-2-one moiety (<b>1</b>), as well as its biosynthetic product (<b>2</b>), and 12 6/6/6/5/6/6/6 heptacyclic derivatives (<b>3</b>-<b>14</b>). 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 ¹H NMR method was established to discriminate 1<i>R</i> and 1<i>S</i> configurations at C-1 of 6/6/6/5/6/6/6 heptacyclic duclauxins according to chemical shift differences of diastereotopic methylene H₂-11 or H₂-12 (Δδ_H-11 or Δδ_H-12). Compounds <b>4</b>, <b>7</b>-<b>8</b>, <b>13</b>-<b>15</b>, and <b>18</b> exhibited moderate inhibition of <i>Arabidopsis thaliana</i> 4-hydroxyphenylpyruvate dioxygenase (<i>At</i>HPPD), with IC₅₀ values ranging from 17.1 to 71.3 μM.