**4. Conclusions**

Ten polysulfated steroids **1**–**10** were isolated from the Vietnamese marine sponge *Halichondria vansoesti*. The structures of seven previously unreported compounds (**1**–**4** and **8**–**10**) were established by 1D- and 2D-NMR spectroscopy, HRESIMS, and chemical transformations. Compounds **1**–**4**, **8**, and **9** are new analogues of topsentiasterol sulfates. The characteristic Δ9(11)-4β-hydroxy-14α-methyl-2β, 3α, 6α-trisulfated steroid nucleus and unusual side chains, not previously described in trisulfated steroids from sponges, were found in the structures of these compounds. Compound **10** is a new analogue of halistanol sulfate, containing a 4β-hydroxy-2β, 3α, 6α-trisulfated steroid nucleus and this is the first report of this structure in sponge polar steroids. We proposed hypothetical pathways for the biosynthesis of the side chains in new topsentiasterol sulfates. Some of the isolated trisulfated steroids were able to suppress PSA expression and glucose uptake in human prostate cancer cells and thus may serve as starting compounds for the development of novel prostate cancer drugs.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/17/8/445/s1, Figure S1: List of the previously described polysulfated steroids, combined into subgroups in accordance with the structural features of the steroid nucleus, Figures S2–S44: Copies of HRESIMS, 1D- and 2D-NMR spectra of **1**–**10**, Figure S45: Structure of codisterol (**12**), Figure S46: Photo of the studied sample of sponge *Halichondria vansoesti* (registration number N 049-232).

**Author Contributions:** K.M.T. isolated the metabolites; T.N.M. and K.M.T. elucidated the structures; S.A.D. performed the PSA expression and glucose uptake assays; V.A.D. performed the NMR spectra; R.S.P. and P.S.D. performed the mass spectra; B.B.G. performed species identification of the sponge; C.B., G.v.A., and N.X.C. assisted the results discussion; K.M.T., T.N.M., and S.A.D. wrote the paper, which was revised and approved by all the authors.

**Funding:** The isolation: the establishment of chemical structures, and the determination of cytotoxic activity were partially supported by Grant No. 18-53-54002 Viet-a from the RFBR and QTRU01.04/18-19 from VAST. The study of the effects of isolated metabolites on the expression of PSA and glucose uptake in human prostate cancer cells was supported by grant No. 18-74-10028 from RSF (Russian Science Foundation).

**Acknowledgments:** We thank Academician Valentin A. Stonik, for reading the manuscript and helpful advices.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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