Speradines F–H, Three New Oxindole Alkaloids from the Marine-Derived Fungus <i>Aspergillus oryzae</i>

Abstract

A rare hexacyclic oxindole alkaloid, speradine F (1), together with two novel tetracyclic oxindole alkaloids, speradines G (2) and H (3), were isolated from the marine-derived fungus Aspergillus oryzae. Their structures were determined by spectroscopic methods and X-ray diffraction analysis. This study is the first report on cyclopiazonic acid (CPA)-type alkaloids with a hexacyclic skeleton.

Aspergillus hancockii sp. nov., a biosynthetically talented fungus endemic to southeastern Australian soils

“…Other than hancockiamides A and E, only a single class of three analogues was observed, having a distinctive UV shape (λ max 220, 264, 314 nm) with diagnostic value. The most abundant analogue of this class was purified and identified as the oxindole, speradine F [29] ( t R 4.82 min, 0.80%; λ max 218, 264, 314 nm; ESIMS m/z [M–H] – 413, [M+H] + 415). HPLC peaks eluting at 3.96 and 4.92 min with similar UV-vis maxima were tagged as putative minor analogues of speradine F, but insufficient material was available for isolation and characterisation.…”

“…Confusingly, speradine F was originally reported from A . oryzae [29], then later as speradine B from A . flavus [32], and again as penicamedine A from Penicillium camemberti [33].…”

Recent Discovery of Heterocyclic Alkaloids from Marine-Derived Aspergillus Species

“…More precisely, compounds 23-29 were isolated from the culture of an epiphytic fungal strain of A. oryzae residing in marine sediments that were collected from Langqi Island, China, while compound 30 was obtained from the culture of a marine isopod-associated endophytic fungus, A. sp. Z-4, which was derived from the marine isopod Ligia oceanica [35][36][37]. Compound 31 was characterized as a new prenylated indole alkaloid, which was isolated from a coculture of the marine-derived fungi A. sulphureus KMM 4640 and Isaria felina KMM 4639 [38].…”

“…Marine-derived fungi could be isolated from every possible marine habitat, such as marine sediments, marine invertebrates (sponges, corals, ascidians, and holothurians), and vertebrates (mainly fish), as well as marine plants (algae, driftwood, and mangrove plants) [74,75]. As shown in Table 1 [46,56,64], while the other strains were collected from marine sediments at depths above 100 m or even tideland mud [28,35,36,40,42,57,65,69,70]. Unfortunately, the source of the producing strain of 31-35 (A. sulphureus KMM 4640 and I. felina KMM 4639) was not described [39].…”

A Ten‐Step Total Synthesis of Speradine C

“…Since 2003, a number of highly oxygenated cyclopiazonic acid (CPA)‐derived alkaloids, such as speradines A–C ( 2 – 4 ) and aspergillines A–E, were isolated and identified (Figure A) . Among them, speradine C ( 4 ) has an extraordinary chemical structure containing an unprecedented 6/5/6/5/5/6 hexacyclic ring system with a 5,6‐dihydroxy‐4‐oxo‐1,3‐oxazinane unit and six stereocenters including four oxygen‐bearing carbon centers.…”