•We isolated novel decalin derivatives from a marine sponge-derived fungus.•Their absolute stereostructures were established by the hydrolysis.•They exhibited potent cytotoxicity against three cancer cell lines.Tandyukisins A–D reported previously, novel decalin derivatives, have been isolated from a strain of Trichoderma harzianum OUPS-111D-4 originally derived from the marine sponge Halichondria okadai, and their structures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques. In addition, their chemical structures were established by chemical transformation. In our continuing search for cytotoxic metabolites from this strain, we isolated two new decalin derivatives designated tandyukisins E (1) and F (2). They have unique chemical structures with different side chains from those of tandyukisins obtained so far. In addition, they exhibited significant cytotoxicity against the cancer cell lines P388, HL-60, and L1210.

•We isolated a novel decalin derivative from a fungal strain derived from the sea urchin.•The stereochemistry for new compound was established by the chemical transformation.•The compound exhibited the moderate cytotoxicity against two cancer cell lines.Altercrasin A (1), a novel decalin derivative with a spiroskeleton, has been isolated from a strain of Alternaria sp. OUPS-117D-1 originally derived from the sea urchin Anthocidaris crassispina, and its structure has been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques. In addition, the absolute configuration for 1 was established by chemical transformation and the modified Mosher’s method. This compound exhibited moderate cytotoxicity against human cancer cell lines.

•We isolated a novel decalin derivative from a fungal strain derived from the marine sponge.•The absolute configuration for new compound was established by the application of CD spectrum.•We examined the cytotoxicity of metabolites having an alkylated decalin skeleton at first.Tandyukisin (1), a novel decalin derivative with an enolic β-ketoaldehyde, has been isolated from a strain of Trichoderma harzianum OUPS-111D-4 originally derived from the marine sponge Halichondria okadai, and its structure has been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques. In addition, the absolute configuration for 1 was established by the application of CD spectrum to the tribenzoate derivative. This compounds exhibited moderate cytotoxicity against human cancer cell lines.

A new metabolite, pileotin A, was isolated from a strain of Aspergillus fumigatus originally obtained from the sea urchin Toxopneustes pileolus together with the known compound oxalicine B. The relative stereostructure of pileotin A was elucidated based on spectroscopic analyses, including 1D and 2D NMR techniques. This unique pyridino-α-pyrone sesquiterpene type metabolite has spiro-δ-lactone at C-4.

Halichoblelide B (1) and C (2), novel macrolides with potent cytotoxicity against tumor cells in culture, have been isolated from a strain of Streptomyces hygroscopicus originally derived from the marine fish Halichoeres bleekeri, and their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques and chemical transformations. These compounds exhibited significant cytotoxicity against human cancer cell lines.

Three new metabolites, chaetomugilin S, dechloro-chaetomugilin A and dechloro-chaetomugilin D, were isolated from a strain of Chaetomium globosum originally obtained from the marine fish Mugil cephalus, and their absolute stereostructures were elucidated based on the basis of spectroscopic analyses, including 1D and 2D NMR techniques and some chemical transformations. Particularly, chaetomugilins T and U are the first compouds without a chlorine atom in azaphilones isolated from this fungal strain, to date. In addition, these compounds moderately inhibited the growth of cultured P388, HL-60, L1210 and KB cell lines.

Four new metabolites, chaetomugilins P–R and 11-epi-chaetomugilin I, were isolated from a strain of Chaetomium globosum originally obtained from the marine fish Mugil cephalus, and their absolute stereostructures were elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR techniques and various chemical transformations. Particularly, the skeleton of chaetomugilin P is different from that of other azaphilones isolated from this fungal strain to date. In addition, these compounds significantly inhibited the growth of cultured P388, HL-60, L1210 and KB cell lines.

Chaetomugilins G and H were isolated from a strain of Chaetomium globosum that was originally isolated from the marine fish, Mugil cephalus, and their absolute stereostructures were elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR techniques, and chemical transformation. In addition, the absolute configuration of chaetoviridin C was established by derivatization from chaetomugilin A. These compounds exhibited a growth inhibitory activity against cultured P388, HL-60, L1210 and KB cells.

Chaetomugilins A~F have been isolated from a strain of Chaetomium globosum originally isolated from the marine fish Mugil cephalus, and their absolute stereostructures have been elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR techniques, some chemical transformations and an X-ray analysis. These compounds exhibited significant growth inhibition against cultured P388 cells and HL-60 cells. In addition, chaetomugilins A, C and F showed selective cytotoxic activities against 39 human cancer cell lines.

Peribysin J and macrosphelide M have been isolated from a strain of Periconia byssoides originally isolated from the sea hare Aplysia kurodai. Their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques and some chemical transformations including the modified Mosher's method. These fungal metabolites inhibited the adhesion of human-leukemia HL-60 cells to human-umbilical-vein endothelial cells (HUVEC).

Peribysins H (1) and I (2) have been isolated from a strain of Periconia byssoides originally separated from the sea hare Aplysia kurodai. Their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques and some chemical transformations including the modified Mosher's method. These metabolites inhibited the adhesion of human-leukemia HL-60 cells to HUVEC.

Peribysins EG (13) have been isolated from a strain of Periconia byssoides originally separated from the sea hare Aplysia kurodai. Their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques and some chemical transformations. In addition, the absolute configuration of peribysin A (4), previously undetermined, has been established by conversion to 2 and 3. All these metabolites inhibited the adhesion of human-leukemia HL-60 cells to HUVEC.