Correction: Marrero et al. Kallopterolides A–I, a New Subclass of seco-Diterpenes Isolated from the Southwestern Caribbean Sea Plume Antillogorgia kallos. Molecules 2024, 29, 2493

• Text Correction

A typographic error involving S* and R* was made in the original publication [1]. A correction has been made to Section 2. Results and Discussion section, specifically in Section 2.1. Chemical Structural Analysis, in the 6th and 7th paragraphs:

This conclusion was validated by the small axial-equatorial coupling constant between these protons (J_H6–H7 = 4.1 Hz). Furthermore, the fixed conformation depicted in Figure 4a was supported by the strong NOESY correlations observed between H-5/Me-16, H-5/H-7, H-7/Me-19, Me-19/H-18β, and H-8/H-18α. Farther along the eastern quadrant, the peak assignment for Me-14 and Me-15 in the ¹H-NMR spectrum of 1 was based on the NOESY cross-peak between H-2 and Me-15. While these methods allowed us to establish the assignments described, we should point out that the relative configuration drawn for 1, namely, 6R*, 7S*, and 8R*, correlates well with the known absolute configuration of other diterpenes co-isolated during this investigation (namely, kallolide A, kallolide A acetate, kallolide C, bipinnapterolide A, and gersemolide). This observation aligns with our contention that, most likely, 1 originates following oxidation/cleavage at C-2/C-3 of a suitable pseudopterane-based precursor (see Figure 1 and Scheme S1 in the Supplementary Materials).

Kallopterolide B (2), an optically active yellowish oil, ${\left[\mathsf{\alpha }\right]}_D^{20}$ +5.0 (c 1.0, MeOH), showed a pseudomolecular [M + 1]⁺ ion peak at m/z 345.1696 in the HR-FAB-MS corresponding to a molecular formula of C₂₀H₂₅O₅ (calcd 345.1702). The IR and UV spectroscopic data for 2 were very similar to those recorded for kallopterolide A (1). Further examination revealed that their ¹H and ¹³C NMR data in CDCl₃ were also almost identical, indicating that both compounds possess identical functionality, namely, two α,β-unsaturated-γ-lactones, one α-substituted-β,β-dimethyl-α,β-unsaturated aldehyde, and one isopropenyl group. Therefore, we concluded that these compounds must be diastereomers. A detailed side-by-side comparison of the ¹H NMR spectra of 1 and 2 (Table 1) revealed that the minor differences observed could be explained by inverting the configuration in 2 at C-6. The reversal at C-6 from R* in 1 to S* in 2 was rendered by subtle differences in the ¹H NMR chemical shifts and coupling constants for H-6 [δ_H 5.34 (ddd, 1H, 3.9, 2.0, 1.9 Hz) in 1 vs. δ_H 5.05 (dd, 1H, 1.7, 1.6 Hz) in 2] and H-7 [δ_H 2.21 (dd, 1H, 10.0, 4.3 Hz) in 1 vs. δ_H 2.60 (dd, 1H, 7.0, 7.0 Hz) in 2] (Table 2).

• Error in Figure

In the original publication, there was a mistake in Scheme S1, Figures 2 and S17 as published. The relative stereochemistry for compound 3 about the C8 stereocenter was drawn incorrectly. The corrected Scheme S1, Figure 2 and Figure S17 appear below.

Scheme S1.

Proposed biogenetic pathways for the formation of the kallopterolides.

Figure 2.

Chemical structures of kallopterolides A–I (1–9).

Figure S17.

1H-NMR spectrum (CDCl3, 300 MHz) of Kallopterolide C (3).

The authors state that the scientific conclusions are unaffected. This correction was approved by the Academic Editor. The original publication has also been updated.