Bioactive Sesterterpenoids from a Korean Sponge Monanchora sp.

Abstract

Chemical investigation of a Korean marine sponge, Monanchora sp., yielded nine new sesterterpenoids (1-9) along with phorbaketals A-C (10-12). The planar structures were established on the basis of NMR and MS analysis, and the absolute configurations of 1-9 were defined using the modified Mosher's method and CD spectroscopic data analysis. Compounds 1-8, designated as phorbaketals D-K, possess a spiroketal-modified benzopyran moiety such as phorbaketal A, and their structural variations are due to oxidation and/or reduction of the tricyclic core or the side chain. Compound 9, designated as phorbin A, has a monocyclic structure and is proposed to be a possible biogenetic precursor of the phorbaketals. Compounds 1-9 were evaluated for cytotoxicity against four human cancer cell lines (A498, ACHN, MIA-paca, and PANC-1), and a few of them were found to exhibit cytotoxic activity.

Spiroketal Formation by Cascade Oxidative Dearomatization: An Ap­proach to the Phorbaketal Skeleton

“…Rho et al proposed that cyclization of geranylfarnesyl pyrophosphate creates the phorbane carbon skeleton, [4] oxidation of which gives the γ-hydroxycyclohexenone 3 (Figure 1). [5] Figure 1. Marine-derived sesterterpenoid natural products.…”

Preparation of cis-γ-Hydroxycarvone Derivatives for Synthesis of Sesterterpenoid Natural Products: Total Synthesis of Phorbin A

“…6 Despite the range of biological activity displayed by the natural products described above, synthetic endeavors toward these compounds have been limited, and only alotaketal A (15) has been successfully synthesized…”

A new family of sesterterpenoids isolated around the Pacific Rim

“…10,29 In terms of structure-activity relationship, this observed potency implies that the spiroketal moiety possessed by the phorbaketals may not be an important feature for anticancer activity.…”

“…4). 10 This was followed by isolation of phorbaketals L-N (27-29) again from the marine sponge Phorbas sp. from South Korean waters.…”

“…Oxidation of alotane (1) at C1, C4 and C9 gives phorbin A (14). This natural product was isolated alongside phorbaketals D-K in 2013 10 and is currently the least elaborated and hence biogenetically the earliest of the known alotane sesterterpenoids. A possible pathway to the common spiroketal-hydrobenzopyran framework may involve epoxidation/rearrangement about C7 and further oxidation of the unsaturated skeleton to form hydroxy ketones (e.g.…”