The discovery of chlorothricin (1) defined a new family of microbial metabolites with potent antitumor antibiotic properties collectively referred to as spirotetronate polyketides. These microbial metabolites are structurally distinguished by the presence of a spirotetronate motif embedded within a macrocyclic core. Glycosylation at the periphery of this core contributes to the structural complexity and bioactivity of this motif. The spirotetronate family displays impressive chemical structures, potent bioactivities, and significant pharmacological potential. This review groups the family members based on structural and biosynthetic considerations and summarizes synthetic and biological studies that aim to elucidate their mode of action and explore their pharmacological potential.

Neurodegenerative diseases and spinal cord injury affect approximately 50 million people worldwide, bringing the total healthcare cost to over 600 billion dollars per year. Nervous system growth factors, that is, neurotrophins, are a potential solution to these disorders, since they could promote nerve regeneration. An average of 500 publications per year attests to the significance of neurotrophins in biomedical sciences and underlines their potential for therapeutic applications. Nonetheless, the poor pharmacokinetic profile of neurotrophins severely restricts their clinical use. On the other hand, small molecules that modulate neurotrophic activity offer a promising therapeutic approach against neurological disorders. Nature has provided an impressive array of natural products that have potent neurotrophic activities. This Review highlights the current synthetic strategies toward these compounds and summarizes their ability to induce neuronal growth and rehabilitation. It is anticipated that neurotrophic natural products could be used not only as starting points in drug design but also as tools to study the next frontier in biomedical sciences: the brain activity map project.

Fusarisetin A (1) is a recently isolated natural product that displays an unprecedented chemical motif and remarkable bioactivities as a potent cancer migration inhibitor. We describe here our studies leading to an efficient and scalable total synthesis of 1. Essential to the strategy was the development of a new route for the formation of a trans-decalin moiety of this compound and the application of an oxidative radical cyclization (ORC) reaction that produces fusarisetin A (1) from equisetin (2) via a bio-inspired process. TEMPO-induced and metal/O2-promoted ORC reactions were evaluated. Biological screening in vitro confirms the reported potency of (+)-1. Importantly, ex vivo studies show that this compound is able to inhibit different types of cell migration. Moreover, the C5 epimer of (+)-1 was also identified as a potent cancer migration inhibitor, while (−)-1 and 2 were found to be significantly less potent. The optimized synthesis is applicable on gram scale and provides a solid platform for analogue synthesis and methodical biological study.

Majucin-type sesquiterpenes from Illicium sp., such as jiadifenolide (2), jiadifenin (3) and (1R,10S)-2-oxo-3,4-dehydroxyneomajucin (4, ODNM), possess a complex caged chemical architecture and remarkable neurotrophic activities. As such, they represent attractive small molecule leads against various neurodegenerative diseases. We present an efficient, enantioselective and unified synthesis of 2, 3 and 4 and designed analogues that diverge from tetracyclic key intermediate 7. The synthesis of 7 is highlighted by the use of an enantioselective Robinson annulation reaction (construction of AB rings), a Pd-mediated carbomethoxylation reaction (construction of C ring) and a one-pot oxidative reaction cascade (construction of D ring). Evaluation of the neurotrophic activity of these compounds led to the identification of several highly potent small molecules that significantly enhanced the activity of nerve growth factor (NGF) in PC-12 cells. Moreover, efforts to define the common pharmacophoric motif suggest that substitution at the C-10 center significantly affects bioactivity, while the hemiketal moiety of 2 and 3 and the C-1 substitution might not be critical to the neurotrophic activity.

The first enantioselective synthesis of (−)-jiadifenin (1), a potent neurite outgrowth promoter isolated from Illicium species, is described. The synthetic strategy builds upon bicyclic motif 6 that represents the AB ring of the natural product and proceeds in 19 steps and 1.1% overall yield. Key to our approach is a Mn(III)-mediated oxidation reaction of A ring that, following a regio- and diastereoselective α-hydroxylation and methylation sequence, produces the desired functionalities of (−)-jiadifenin. The effect of synthetic 1 in NGF-mediated neurite outgrowth was also measured in PC-12 cells.