Bryophytes frequently grow in an unfavorable environment as the earliest land plants, and inevitably biosynthesize secondary metabolites against biotic or abiotic stress. They not only defend against the plant competition, microbial attack, and insect or animal predation, but also function in UV protection, drought tolerance, and freezing survival. This review covers the ecological aspect of secondary metabolites in bryophytes and is taxonomically presented according to the ecological significances.

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Ten myrsinol diterpenes, euphorbiaproliferins A-J (1-10), along with nine known analogues (11-19) were isolated from the roots of Euphorbia prolifera. Their structures were elucidated by spectroscopic data analysis (IR, ESIMS, HRESIMS, 1D and 2D NMR), and the structure of 1 was confirmed by X-ray crystallography. The diterpenes showed neuroprotective effects against MPP+-induced neuronal cell death in SH-SY5Y cells.

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Eight new clerodane diterpenes, balanspenes A-H (1-8), along with two known analogues (9 and 10), were isolated from the twigs of Casearia balansae. The structures of 1-8 were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analysis, and the absolute configurations of compounds 1, 4, and 7 were confirmed by comparing their experimental CD spectra with those calculated by the time-dependent density functional theory method. Compounds 4-7, 9, and 10 were found to possess the property of being able to stimulate NGF-mediated neurite outgrowth from PC12 cells.

Three new rearranged ent-kaurane-type diterpenoids (1-3) and seven new ent-kaurane-type diterpenoids (4-10) have been isolated from the liverwort Jungermannia atrobrunnea. Their structures were determined by extensive spectroscopic techniques and X-ray crystallographic analysis. The absolute configurations of these compounds were clarified by CD spectroscopic studies. Compound 1 is the first example of a rearranged ent-kaurane diterpenoid possessing a peroxide bridge.

Pallambins A (1) and B (2), two novel 19-nor-7,8-secolabdane diterpenoids with unprecedented tetracyclo[4.4.0(3,5).0(2,8)]decane skeletons, along with a pair of structurally related isomers, pallambins C (3) and D (4), were isolated from the Chinese liverwort Pallavicinia ambigua. Their structures with absolute configurations were determined by means of NMR, X-ray diffraction, and CD analyses. Their preliminary cytotoxicity to human cancer cells was also tested.