Dictyoptesterols A-C, ∆22-24-oxo cholestane-type sterols with potent PTP1B inhibitory activity from the brown alga Dictyopteris undulata Holmes.

Three new cholestane-type sterols bearing an unusual ∆22-24-oxo side chain, namely, dictyoptesterols A-C (1-3), were isolated from the brown alga Dictyopteris undulata Holmes, together with five known strutural analogues (4-8). Their structures were elucidated on the basis of by extensive spectroscopic analysis. The absolute configurations of the steroidal nuclei of the new compounds were proposed by a comparison of NMR data with those of related known compounds as well as biogenetic considerations. All of the isolates were evaluated in vitro for their potential to inhibit protein tyrosine phosphatase-1B (PTP1B) activity. The results showed that compounds 1-5 exhibited different levels of PTP1B inhibitory activities with IC50 values ranging from 3.03 ±â€¯0.76 to 15.01 ±â€¯2.88 µM. In particular, compounds 3 and 4 showed promising inhibitory effects towards PTP1B with IC50 values of 3.03 ±â€¯0.76 and 3.72 ±â€¯0.40 µM, respectively, when compared to the positive control oleanolic acid (IC50, 2.83 ±â€¯0.39 µM). The chemotaxonomic significance of these isolated ∆22-24-oxo cholestanes has also been discussed.

PTP1B inhibitory and cytotoxic C-24 epimers of Δ28-24-hydroxy stigmastane-type steroids from the brown alga Dictyopteris undulata Holmes.

Ten stigmastane-type steroids bearing unusual Δ28-24-hydroxy side chains, dictyopterisins A-J, including three pairs of C-24 epimers, dictyopterisins B/C, F/G, and I/J, were isolated from the brown alga Dictyopteris undulata Holmes, together with two previously reported analogues, (24S)- and (24R)-saringosterol. Their structures were elucidated on the basis of extensive spectroscopic analysis, with their absolute configurations at the stereogenic center C-24 of the side chain being assigned by a direct comparison of 1H NMR data with those of related known compounds. The absolute configurations of the steroidal nuclei of dictyopterisins A, B, and H were determined using the modified Mosher's method. The mixture of dictyopterisins D and E and dictyopterisin I exhibited promising PTP1B inhibitory activities with IC50 values of 1.88 and 3.47 µM, respectively, comparable to the positive control oleanolic acid (IC50, 2.78 µM). In addition, the mixture of dictyopterisins D and E and dictyopterisins F-J displayed significant cytotoxicities against the human cancer cell lines HL-60 (IC50 from 1.02 to 2.70 µM) and A-549 (IC50 from 1.35 to 2.85 µM).

New isoquinolinequinone alkaloids from the South China Sea nudibranch Jorunna funebris and its possible sponge-prey Xestospongia sp.

Two new renieramycin-type bistetrahydroisoquinolinequinone alkaloids, fennebricins A (1) and B (5), and one new isoquinolinequinone alkaloid, N-formyl-1,2-dihydrorenierol (7), were isolated from the skin of the South China Sea nudibranch Jorunna funebris and its possible sponge-prey Xestospongia sp., together with eight known metabolites, including three bistetrahydroisoquinolinequinones (2-4) and five isoquinolinequinones (8-12). Their structures were elucidated by analysis of spectroscopic data including 1D and 2D NMR and high-resolution electrospray ionization mass spectrometry (HRESIMS) and by comparison with data for related known compounds. All the metabolites except for 7 occurred simultaneously in the two animals, supporting recent ecological studies that the nudibranch J. funebris preys on the sponge of the genus Xestospongia.

A seco-laurane sesquiterpene and related laurane derivatives from the red alga Laurencia okamurai Yamada.

A ring-cleaved sesquiterpene, named seco-laurokamurone, four laurane-type sesquiterpenes, laurepoxyene, 3ß-hydroperoxyaplysin, 3α-hydroperoxy-3-epiaplysin, and 8,10-dibromoisoaplysin, one laurokamurane-type sesquiterpene, laurokamurene D, and one bisabolane-type sesquiterpene, (5S)-5-acetoxy-ß-bisabolene, have been isolated from a re-collection of the red alga Laurencia okamurai Yamada, together with six other known sesquiterpenes. Their structures, including relative configuration, were elucidated by detailed analysis of spectroscopic data, and by comparison with data for related known compounds. In addition, on the basis of chemical conversions, degradation results, and biogenetic considerations, the absolute configurations of several of these compounds were also tentatively proposed. seco-Laurokamurone possesses an unprecedented carbon skeleton, formed from an oxidative cleavage of the laurokamurane skeleton, and laurokamurene D represents the fourth example of a laurokamurane-type sesquiterpene from a natural source. The in vitro antifungal activity of many of these compounds was evaluated against four fungi (Cryptococcus neoformans, Candida glabrata, Trichophyton rubrum, and Aspergillus fumigatus), as well as assessing cytotoxicity against HL-60 and A-549 human cancer cell lines. The compounds studied displayed moderate activities, relative to controls.

Racemosins A and B, two novel bisindole alkaloids from the green alga Caulerpa racemosa.

Racemosin A (1), a structurally unique bisindole alkaloid possessing the seco-indolo[3,2-a]carbazole skeleton with two uncommon indolinenone units both conjugated with a methyl propenoate moiety, and its unusual cyclized derivative, racemosin B (2), were isolated from the green alga Caulerpa racemosa, together with the most commonly encountered pigment in the genus Caulerpa, caulerpin (3). Their structures were elucidated by extensive spectroscopic analysis and by comparison with data for related known compounds. A plausible biosynthetic pathway of 1 and 2 was proposed. In a neuro-protective assay, compound 1 significantly attenuated the Aß2(5-35)-induced SH-SY5Y cell damage with a 14.6% increase in cell viability at the concentration of 10µM when compared to epigallocatechin gallate (EGCG, 16.57% increase at 10 µM) as the positive control.

Caulerprenylols A and B, two rare antifungal prenylated para-xylenes from the green alga Caulerpa racemosa.

Two new prenylated para-xylenes, named caulerprenylols A (1) and B (2), were isolated from the green alga Caulerpa racemosa, collected from the Zhanjiang coastline, China. The structures of the two metabolites were elucidated on the basis of detailed spectroscopic analysis. This is the first report of prenylated para-xylenes from marine algae and from marine organisms as well. Moreover, caulerprenylol B (2) is also characterized by an uncommon indane ring system. In in vitro bioassays, the new compounds exhibited a broad spectrum of antifungal activity against Candida glabrata (537), Trichophyton rubrum (Cmccftla), and Cryptococcus neoformans (32609) with MIC80 values between 4 and 64 µg/mL when compared to amphotericin B (MIC80 values of 2.0, 1.0, and 4.0 µg/mL, respectively) as a positive control and showed no growth inhibition activity against the tumor cells HL60 and A549.