The fungus Xylaria sp. KYJ-15 was isolated from Illigera celebica. Based on the one strain many compounds (OSMAC) strategy, the strain was fermented on potato and rice solid media, respectively. As a result, two novel steroids, xylarsteroids A (1) and B (2), which are the first examples of C28-steroid with an unusual β- and γ-lactone ring, respectively, along with two new dihydroisocoumarin glycosides, xylarglycosides A (3) and B (4), were identified. Their structures were elucidated by spectroscopic methods, X-ray diffraction and electronic circular dichroism (ECD) experiments. All isolated compounds were evaluated for cytotoxicity, DPPH radical scavenging activity, acetylcholinesterase inhibitory and antimicrobial effect. Compound 1 exhibited potent AChE inhibitory activity with an IC50 value of 2.61 ± 0.05 μmol·L-1. The β-lactone ring unit of 1 is critical for its AChE inhibitory activity. The finding was further confirmed through exploring the interaction of 1 with AChE by molecular docking. In addition, both compounds 1 and 2 exhibited obvious antibacterial activity against Bacillus subtilis with a minimum inhibitory concentration (MIC) of 2 μg·mL-1. Compounds 3 and 4 exhibited antibacterial activities against Staphylococcus aureus with MICs of 4 and 2 μg·mL-1, respectively, which also exhibited DPPH radical scavenging activity comparable to the positive control with IC50 values of 9.2 ± 0.03 and 13.3 ± 0.01 μmol·L-1, respectively.

bioactivity, secondary metabolite, Xylaria sp., OSMAC strategy

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10
4,4	Me	59.6
4	bDManp	96.6	71.1	73.8	77.1	76.2	61.3
	Subst	167.9	79.6	71.6	135.4	120.4	136.2	118.3	161.9	107.2	16.5


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9	H10
4,4	Me	3.35
4	bDManp	4.34	3.69	3.45	3.28	3.20	3.76-3.92
	Subst	-	5.12	4.98	-	7.05	7.61	7.07	-	-	1.32


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9	C10/H10
4,4	Me	59.6/3.35
4	bDManp	96.6/4.34	71.1/3.69	73.8/3.45	77.1/3.28	76.2/3.20	61.3/3.76-3.92
	Subst		79.6/5.12	71.6/4.98		120.4/7.05	136.2/7.61	118.3/7.07			16.5/1.32

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CO[C@@H]1[C@@H](CO)O[C@@H](OC2c3cccc(O)c3C(=O)O[C@H]2C)[C@@H](O)[C@H]1O

370.354 g/mol (C₁₇H₂₂O₉)

The fungus Xylaria sp. KYJ-15 was isolated from Illigera celebica. Based on the one strain many compounds (OSMAC) strategy, the strain was fermented on potato and rice solid media, respectively. As a result, two novel steroids, xylarsteroids A (1) and B (2), which are the first examples of C28-steroid with an unusual β- and γ-lactone ring, respectively, along with two new dihydroisocoumarin glycosides, xylarglycosides A (3) and B (4), were identified. Their structures were elucidated by spectroscopic methods, X-ray diffraction and electronic circular dichroism (ECD) experiments. All isolated compounds were evaluated for cytotoxicity, DPPH radical scavenging activity, acetylcholinesterase inhibitory and antimicrobial effect. Compound 1 exhibited potent AChE inhibitory activity with an IC50 value of 2.61 ± 0.05 μmol·L-1. The β-lactone ring unit of 1 is critical for its AChE inhibitory activity. The finding was further confirmed through exploring the interaction of 1 with AChE by molecular docking. In addition, both compounds 1 and 2 exhibited obvious antibacterial activity against Bacillus subtilis with a minimum inhibitory concentration (MIC) of 2 μg·mL-1. Compounds 3 and 4 exhibited antibacterial activities against Staphylococcus aureus with MICs of 4 and 2 μg·mL-1, respectively, which also exhibited DPPH radical scavenging activity comparable to the positive control with IC50 values of 9.2 ± 0.03 and 13.3 ± 0.01 μmol·L-1, respectively.

bioactivity, secondary metabolite, Xylaria sp., OSMAC strategy

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10
4	bDManp	98.4	71.9	73.3	72.9	?	60.8
	Subst	168.1	78.4	73.6	137.0	120.7	136.7	117.9	162.3	107.4	16.8


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9	H10
4	bDManp	5.11	3.36	3.44	3.22	3.23	3.51
	Subst	-	5.04	4.65	-	7.01	7.49	6.92	-	-	1.22


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9	C10/H10
4	bDManp	98.4/5.11	71.9/3.36	73.3/3.44	72.9/3.22	?/3.23	60.8/3.51
	Subst		78.4/5.04	73.6/4.65		120.7/7.01	136.7/7.49	117.9/6.92			16.8/1.22

The spectrum also has 1 signal at unknown position (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

C[C@@H]1OC(=O)c2c(O)cccc2C1O[C@@H]1O[C@H](CO)[C@@H](O)[C@H](O)[C@@H]1O

356.327 g/mol (C₁₆H₂₀O₉)