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H. Zhu et al.
oxidative cleavage of the C-19-C-20 bond. Later, the same group discovered two
new seco-chaetoglobosins, armochaetoglasins B and C (331 and 332) [10], from the
above-mentioned fungal source. Moreover, Ding and coworkers also isolated a 19,20seco-chaetoglobosin named yamchaetoglobosin A (333) [151] from Chaetomium
globosum YNH-16. Thus, all of these seco-chaetoglobosins were discovered from
the fungus Chaetomium globosum of different origins.
2.3.3 Mero-chaetoglobosins
In 2013, Shin-ya and coworkers reported three novel metabolites including MBJ0038 (334), MBJ-0039 (335), and MBJ-0040 (336) from Chaetomium sp. f24230
collected from a soil sample [152]. The structures of these compounds are closely
related to those of normal chaetoglobosins; however, they have an additional unit
(known as epicoccine) fused to C-21 and C-22, exhibiting a complicated ring system.
They are the first examples of mero-chaetoglobosins, but regrettably, no biosynthesis pathway was proposed for these metabolites and their configurations were not
determined.
In 2018, aureochaeglobosins A–C (340–342) [153], three novel [4 + 2] cycloaddition heterodimers of chaetoglobosin and aureonitol derivatives, were obtained from
a culture of the endophytic fungus Chaetomium globosum, which also represent a
new type of mero-chaetoglobosins. Their structures were elucidated by extensive
spectroscopic data analysis as well as by single-crystal X-ray diffraction and the use
of the modified Mosher’s method.
In the same year, cytochathiazines A–C (337–339) [154], which represent a
new type of mero-chaetoglobosins, were isolated from a coculture of Chaetomium
globosum and Aspergillus flavipes. These are the first natural products featuring
an unprecedented 2H-1,4-thiazine functional group, and a plausible biosynthesis
pathway with a chaeto-globosin molecule and a dipeptide as the main constitutional
units was proposed [154].
2.4 The Aspochalasin Group
Aspochalasins are the third-largest group of cytochalasans that feature the incorporation of leucine into a polyketide backbone (Tables 15, 16, 17, 18 and 19 and Figs. 15,
16, 17, 18 and 19). In this section, 127 aspochalasins are included (343–469), and,
similar to the cytochalasins and pyrichalasins, most aspochalasins possess a [5.6.11]
tricyclic ring system. In terms of their ring C, aspochalasins normally possess a double
bond at C-13, a methyl group at C-14, and a carbonyl group at C-21. Xylarisin (360)
[155] is the only example of an aspochalasin exhibiting a [5.6.11] ring system, and
is without a methyl group at C-14. This was isolated from the marine-derived fungus
Xylaria sp. PSU-F100 by Rukachiaisirikul and coworkers in 2009.
H. Zhu et al.
oxidative cleavage of the C-19-C-20 bond. Later, the same group discovered two
new seco-chaetoglobosins, armochaetoglasins B and C (331 and 332) [10], from the
above-mentioned fungal source. Moreover, Ding and coworkers also isolated a 19,20seco-chaetoglobosin named yamchaetoglobosin A (333) [151] from Chaetomium
globosum YNH-16. Thus, all of these seco-chaetoglobosins were discovered from
the fungus Chaetomium globosum of different origins.
2.3.3 Mero-chaetoglobosins
In 2013, Shin-ya and coworkers reported three novel metabolites including MBJ0038 (334), MBJ-0039 (335), and MBJ-0040 (336) from Chaetomium sp. f24230
collected from a soil sample [152]. The structures of these compounds are closely
related to those of normal chaetoglobosins; however, they have an additional unit
(known as epicoccine) fused to C-21 and C-22, exhibiting a complicated ring system.
They are the first examples of mero-chaetoglobosins, but regrettably, no biosynthesis pathway was proposed for these metabolites and their configurations were not
determined.
In 2018, aureochaeglobosins A–C (340–342) [153], three novel [4 + 2] cycloaddition heterodimers of chaetoglobosin and aureonitol derivatives, were obtained from
a culture of the endophytic fungus Chaetomium globosum, which also represent a
new type of mero-chaetoglobosins. Their structures were elucidated by extensive
spectroscopic data analysis as well as by single-crystal X-ray diffraction and the use
of the modified Mosher’s method.
In the same year, cytochathiazines A–C (337–339) [154], which represent a
new type of mero-chaetoglobosins, were isolated from a coculture of Chaetomium
globosum and Aspergillus flavipes. These are the first natural products featuring
an unprecedented 2H-1,4-thiazine functional group, and a plausible biosynthesis
pathway with a chaeto-globosin molecule and a dipeptide as the main constitutional
units was proposed [154].
2.4 The Aspochalasin Group
Aspochalasins are the third-largest group of cytochalasans that feature the incorporation of leucine into a polyketide backbone (Tables 15, 16, 17, 18 and 19 and Figs. 15,
16, 17, 18 and 19). In this section, 127 aspochalasins are included (343–469), and,
similar to the cytochalasins and pyrichalasins, most aspochalasins possess a [5.6.11]
tricyclic ring system. In terms of their ring C, aspochalasins normally possess a double
bond at C-13, a methyl group at C-14, and a carbonyl group at C-21. Xylarisin (360)
[155] is the only example of an aspochalasin exhibiting a [5.6.11] ring system, and
is without a methyl group at C-14. This was isolated from the marine-derived fungus
Xylaria sp. PSU-F100 by Rukachiaisirikul and coworkers in 2009.