Osthole: A Coumarin with Dual Roles in Biology and Chemistry

Simple Summary

Osthole is a natural coumarin-like compound isolated from various plant species. Osthole and its derivatives have received much attention due to their lots of interesting biological activities. In order to timely summarize their recent advances on biology and chemistry from 2018 to early 2025, here the biological activities, mechanisms of action, total synthesis, structural modifications, structure–activity relationships (SARs) of osthole and its derivatives are presented. Hopefully, this review can be used as the useful reference for researchers interested in the biology and chemistry of osthole derivatives for further in-depth research.

Abstract

Osthole is a natural coumarin-like compound isolated from the Fructus cnidii. In the last few years, this plant-derived product and its derivatives have aroused much attention for their interesting biological activities, including anticancer, anti-inflammatory, neuroprotective, and insecticidal effects. This review summarizes the recent progress on the biological activities of osthole and its derivatives from 2018 to early 2025, with a focus on their total synthesis, structural modifications, and mechanisms of action. Additionally, structure–activity relationships (SARs) of osthole derivatives are presented. This review aims to serve as a comprehensive reference for future research on osthole and its derivatives in both medicinal and agricultural applications.

1. Introduction

Coumarin (Figure 1), which contains a 2 H-benzopyran-2-one core structure, is a naturally occurring compound with an aromatic odor that is widely distributed in various plant species. Vogel first isolated it from tonka beans (Dipteryx odoranta Wild; Fabaceae family) in 1820. Since then, thousands of natural coumarins have been isolated, described, and synthesized, and their biological activities have been studied from a variety of sources, including plants, bacteria, fungi, and chemical synthesis [1]. Osthole (1, Figure 1), often referred to as osthol (7-methoxy-8-(3-methyl-2-butenyl) coumarin), is a coumarin analog that was initially isolated from the Cnidium plant [2]. Osthole has shown many biological properties, including anticancer [3], anti-inflammatory [4], osteogenic [5], and neuroprotective activities, without significant toxic side effects [6]. It also has insecticidal activity in agriculture [7].

In this paper, recent advances on biological activities, total synthesis, and structural modifications of osthole and its derivatives from 2018 to early 2025 were reviewed. In addition, their structure–activity relationships (SARs) and mechanisms of action were presented for further in-depth research.

2. Bioactivities of Osthole and Its Derivatives

The biological activities of osthole and its derivatives are outlined in Figure 2.

2.1. Anticancer Activity

Osthole has broad-spectrum anticancer activities against a range of tumor cells (

Table 1. The anticancer activity of osthole.

Tumor	Cell Lines/Model	Involved Mechanism	Period (h)	IC50 (µM)
Endometrial carcinoma	JEC, Ishikawa and KLE cells	Suppressing the proliferation and inducing apoptosis via inhibiting the PI3K/AKT signaling pathway	\	\ [8]
Breast cancer	4T1 cells	Inhibiting cell proliferation, blocking the cells from remaining in S-phase, and inducing apoptosis	48	178.40 [11]
	MDA-MB-231 cells	Inducing apoptosis arrest by elevation in the translation level of p53/Bax/caspase-3 p17 and downregulating of the Bcl-2 protein	\	\ [12]
	MDA-MB-231 cells BT-549 cells MDA-MB-468 cells MCF-7 cells	Inducing apoptosis and cell cycle arrest in TNBC cells through inhibition of STAT3 phosphorylation and nuclear translocation	24	129.40 [10]
				106.20 [10]
				105.40 [10]
				168.00 [10]
	MDA-MB-231 MDA-MB-231BO MCF-7 cells	Inhibiting cell migration and invasion via suppressing of ITGα3 and ITGβ5 signaling	24	29.8 [9]
				111.4 [9]
				260.6 [9]
	BT-474 and MCF-7 cells	Inducing cell cycle arrest, mitochondrial dysfunction, and ER stress	\	\ [13]
Ovarian carcinoma	A2780 cell OVCAR3 cell	Inducing LC3-mediated autophagy and GSDME-dependent pyroptosis	24	75.24 [15]
				73.58 [15]
	ES2 and OV90 cells	Targeting PI3K/MAPK signaling pathway	\	\ [14]
Colorectal cancer	HCT116 and HT29 cells	Regulating autophagy- and mitochondria-mediated signal transduction.	\	\ [17]
	HT-29 cells	Inducing apoptosis via cycle arrest and activating the intrinsic apoptotic pathway	24	115.08 [18]
	HCT116 and SW480 cells	Inhibits malignant phenotypes and inducing ferroptosis in KRAS mutant cells via suppressing AMPK/Akt signaling	\	\ [19]
	CCL-222 cells	Reducing the Akt mRNA expression and the activity p38 MAPK-α	24	23.00 [16]
Colorectal cancer	HT-29 cells	Inducing apoptosis of the cells via endoplasmic reticulum stress and autophagy	\	\ [20]
Hepatocellular carcinoma	HCC-LM3 cells	Inhibiting GSK-3β/AMPK/mTOR pathway-controlled glycolysis	\	[21]
	AKT/c-Met-driven HCC mouse model	Delaying hepatocarcinogenesis by suppressing AKT/FASN axis and ERK phosphorylation	\	[22]
	Huh7 and HepG2 cells	Resensitizing CD133+ hepatocellular carcinoma cells to cisplatin treatment via PTEN/AKT pathway	\	[24]
	Hepa1–6 cells	Inhibiting angiogenesis in an orthotopic mouse model of HCC via the NF-κB/VEGF signaling pathway.	\	[23]
Bladder cancer	5637 cells 253 J cells	Inhibiting invasion, migration, and epithelial–mesenchymal transition by inhibiting PI3K-AKT and JAK/STAT3 pathways	24	146.40 [25] 160.80 [25]
Retinoblastoma	Y-79 cells	Inhibiting the PI3K/AKT/mTOR pathway via regulating the hsa_circ_0007534/miR-214-3p axis	24	200.00 [26]
Cervical cancer	Hela B cells	Targeting DCLK1 mechanistically via interacting with Val468.	\	\ [28]
	CDDP-resistant cervical cancer cells	Reversing chemoresistance of CDDP-resistant cervical cancer to CDDP through repressing NRF2 expression partly associated with PI3K/AKT blockage	\	\ [29]
	HeLa, SiHa, C-33A and CaSki cells	Suppressing ATM/NF-κB signaling	\	\ [27]
Head and neck squamous cell carcinoma	FaDu cells Cal27 cells SCC25 cells HN4 cells	Inducing cell cycle arrest and apoptosis via suppressing the PI3K/AKT signaling pathway	24	122.35 [30] 183.32 [30] 189.26 [30] 237.42 [30]
Glioma	U87 and C6 cells	Triggering glioma cell necroptosis via ROS overproduction	\	\ [31]
	MOGGCCM and T98G cells	Inhibiting of anti-apoptotic Bcl-2 expression, decreasing mitochondrial membrane potential, and activation of caspase 3 via the mitochondrial (internal) pathway	\	\ [32]
	AA and GBM cells	Increasing the level of apoptosis via blocking of the expression of Bcl-2 and PI3K	\	\ [33]
Gallbladder cancer	NOZ and SGC-996 cells	Inhibiting the progression of human gallbladder cancer cells via the JAK/STAT3 signal pathway	\	\ [34]
Lung cancer	A549 cells	Inducing the apoptosis in A549 cells by inhibiting the histone deacetylase	24	188.50 [35]
Gastric cancer	HGC-27 and SGC-7901 cells	Inducting cell cycle arrest at G2/M phase by the regulation of PI3K/AKT	\	\ [36]
	N87 and SK-BR-3 cells	Inducing apoptosis and inhibiting AKT/MAPK pathway	\	\ [37]
Esophageal squamous cell carcinoma	KYSE150 cells KYSE410 cells	Inhibiting the PI3K/AKT signaling pathway via activation of PTEN	24	198.45 [38] 235.67 [38]
Rhabdomyosarcoma	TE671 cells	Inhibiting of cell cycle progression and inducing of apoptosis via the AKT and ERK kinase signaling pathways	96	4.05 * [39]
Pancreatic cancer	Panc 02 cells and RAW 264.7 cells	Attenuating tumor-infiltrating M2 macrophages	\	\ [40]
Nasopharyngeal cancer	NPC-039 and NPC-BM cells	Inducing apoptosis mediated by the Fas-Fas ligand and mitochondrial pathway	\	\ [41]

* µg/mL.

), including endometrial carcinoma (EC) cells [8], breast cancer cells [9,10,11,12,13], ovarian carcinoma (OC) cells [14,15], colorectal (CRC) cancer cells [16,17,18,19,20], hepatocellular carcinoma (HCC) cells [21,22,23,24], bladder cancer cells [25], retinoblastoma (RB) cells [26], cervical cancer cells [27,28,29], head and neck squamous cell carcinoma (HNSCC) cells [30], glioma cells [31,32,33], gallbladder cancer (GBC) cells [34], lung cancer cells [35], human gastric cancer cells [36,37], esophageal squamous cell carcinoma (ESCC) cells [38], rhabdomyosarcoma (RMS) cells [39], pancreatic cancer cells [40], and nasopharyngeal cancer (NPC) cells [41]. Osthole can inhibit the PI3K/Akt signaling pathway in various cancer cells, such as in endometrial carcinoma, bladder cancer, retinoblastoma, cervical cancer, head and neck squamous cell carcinoma, and gastric cancer, which causes cancer cell proliferation, migration, invasion, and death [25,26,27,29,30,36]. Osthole has inhibited 4T1 cell proliferation through mTOR/SREBP1/FASN signaling, blocked cell entry into s phase, and induced apoptosis in breast cancer cells [11]. It can decrease the ASC/caspase-1/IL-1β inflammasome pathway and control colorectal cancer progression by regulating autophagy and mitochondrial signaling [17]. Osthole has inhibited glycolysis regulated by the GSK-3β/AMPK/mTOR pathway, increasing radiosensitivity of subcutaneously transplanted hepatocellular carcinoma in nude mice [21].

2.2. Immunomodulatory and Anti-Inflammatory Activities

Natural products offer several benefits, including the regulation of immune cell differentiation, mitigation of oxidative stress, and a reduction in inflammation. Osthole has acted on DSS-induced UC and LPS-induced ALI in mice by regulating p38 and JNK phosphorylation in the MAPK pathway [42]. Osthole has the potential to treat polycystic ovarian syndrome in mice by activating the Nrf2-Foxo1-GSH-NF-κB pathway [43]. Osthole can effectively prevent DSS-induced ulcerative colitis (UC) and LPS-induced acute lung injury (ALI) [42,44] and inhibit oleic acid/lipopolysaccharide-induced lipid accumulation and inflammatory response in hepatocytes via activating the PPARα signaling pathway [45,46]. Oshtole can treat rheumatoid arthritis (RA) and suppress knee osteoarthritis (KOA) by enhancing autophagy activated by the AMPK/ULK1 pathway [47,48,49,50]. Osthole significantly reduced skin damage and chronic itching associated with atopic dermatitis (AD) by increasing ZO-3 expression and blocking Akt phosphorylation in an AD mouse model [51,52,53,54], as well as having a protective effect against lipopolysaccharide-induced inflammation in BV2 cells [55,56]. Oshthole can ameliorate neurogenic and inflammatory nociceptive sensitization through the modulation of iNOS, COX-2, and inflammatory cytokines, and reduce the role of COX-2 in inflammation and ASD development [57,58].

2.3. Neuroprotective Effects

Osthole has had a neuroprotective impact on Alzheimer’s disease. Intranasal administration of osthole/borneols thermosensitive gel enhanced intracerebral bioavailability and reduced cognitive impairment in APP/PS1 transgenic mice [59,60,61,62]. Osthole can effectively reduce Parkinson’s disease symptoms by inhibiting JAK/STAT and MAPK pathways through attenuating 6-OHDA cytotoxicity in SH-SY5Y cells [63,64,65]. Osthole may delay neural stem cell (NSC) senescence through the p16-pRb signaling pathway [66]. Osthole provided protection against mechanical brain injury, effectively promoted cognitive dysfunction and neuronal recovery, and improved neurological function [67]. Osthole showed a substantial ability to lessen seizures [68]. Osthole reduced pain depression by inhibiting inflammation and oxidative stress-mediated neurotransmitter dysregulation [69].

2.4. Osteogenic Effects and Cardiovascular Benefits

Osthole may be used therapeutically to prevent osteoporosis [70]. Osthole has promoted osteogenic differentiation and inhibited osteoclastogenesis and osteoblast activity [71,72,73]. Osthole has been shown to have cardioprotective properties [74,75], and it can promote autophagy and protect rats from cardiac ischemia/reperfusion injury [76,77].

2.5. Hepatoprotective Effects and Therapeutic Potential in Metabolic Disease

Osthole has protected against D-Gal-induced liver injury through TLR4/MAPK/NF-κB pathways, and also prevented tamoxifen- and acetaminophen-induced liver injury [78,79,80]. Osthole has inhibited renal fibrosis through the IL-11/ERK1/2 signaling pathway, which is independent of TGF-β1 signaling [81,82]. Osthole has had the potential to help prevent and treat diabetic kidney disease (DKD) [83].

2.6. Antimicrobial and Antiparasitic Activities

Osthole has demonstrated inhibitory effects against a wide range of viruses, bacteria, and parasites. Natural products represent valuable sources of novel antimicrobial agents. Against Listeria monocytogenes, osthole strongly decreased Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase activities, increased the production of reactive oxygen species (ROS), and disrupted the integrity and permeability of cell membranes [84,85,86]. Osthole has been successfully developed for its significant inhibitory effect on phytopathogenic fungi (

Table 2. Antibacterial and antifungal activities of osthole.

Object	Period (h)	Values (µg/mL)
Listeria monocytogenes ATCC19115	6	MIC = 62.5 [85]
Staphylococcus aureus ATCC25923	20–24	MIC = 128 [84]
Escherichia coli ATCC25922		MIC = 128 [84]
Staphylococcus aureus (MRSA) ATCC33591		MIC = 128 [84]
Staphylococcus aureus (Methicillin-resistant isolate) ATCC43300		MIC = 128 [84]
Erwinia carotorora	48	98.00% 1 [84]
Ralstonia solanacearum		25.00% 1 [84]
Pseudomonas syringae pv. actinidiae		68.00% 1 [84]
Fusarium oxysporum	72	57.40% 2 [86]
Fusarium moniliforme J. Sheld		70.66% 2 [86]
Thanatephorus cucumeris Donk		75.90% 2 [86]
Penicillium choerospondiatis	144	EC50 = 9.86 [89]
Ustilaginoidea virens	240	EC50 = 5.04 [88]
Fusarium oxysporum	168	EC50 = 6.40 [87]
Cercospora sorghi	72	EC50 = 1.46 [90]

¹ At 0.1 mg/mL; ² At 5 mg/mL.

) [87,88,89,90]. Osthole can effectively inhibit SARS-CoV-2 as well as tobacco mosaic virus (TMV) infection [91,92]. Furthermore, osthole demonstrated a high activity against Rhipicephalus sanguineus [93].

2.7. Insecticidal Activity

Osthole and its derivatives have shown pesticidal effects on Mythimna separata, Myzus persicae, Tetranychus cinnabarinus, and Plutella xylostella Linnaeus [94,95,96]. It can also be a strong attractant for oviposition on Bactrocera dorsalis [97]. Osthole had a significant lethal effect on the second instar larvae of Spodoptera frugiperda [98]. Tetranychus urticae Koch can be controlled by combining matrine and osthole in a certain ratio [99]; osthole had good contact and stomach poisoning effects on Coptotermes formosanus, Sitophilus zeamais Motschusky, and Plutella xylostella Linnaeus [100,101,102]. After treatment of osthole at 125 × 10⁻³ mg/mL for 24 h, the glutathione-S-transferase (GST) and acetylcholinesterase (AChE) activities in the P. xylostella larvae were significantly reduced. Furthermore, osthole showed larvicidal activity against mosquitoes [7,103].

2.8. Other Activities

Osthole can exert antipruritic effects by inhibiting or desensitizing cation channels TRPV1 and TRPV3 [104,105]. Osthole inhibited phosphodiesterase 4D activity, making it a promising bronchodilator for asthma treatment without targeting β2-adrenoceptors [106,107]. Osthole can also dramatically lower blood pressure by inhibiting the vascular constriction mediated by angiotensin II and CaCl₂ [108].

3. Total Synthesis of Osthole and Its Derivatives

As described in Scheme 1, Liu et al. reported the synthesis of osthole (1) by 8-allyl-7-methoxycoumarin olefin complexation using 2,4 dihydroxybenzaldehyde (2) as a raw material [109]. Compound 3 was formed by reacting compound 2 with ethyl 2-chloroacetate. Subsequently, in the presence of potassium carbonate and potassium iodide, compound 3 was reacted with 3-chloropropene to afford compound 4, which was then C-8 Claisen rearranged to give compound 5. Compound 5 was methylated with dimethyl sulfate in acetone to give compound 6. Ultimately, compound 1 was created with a 77.6% yield by reacting compound 6 with 3-chloro-3-methyl-1-butylene. Meanwhile, Yin et al. developed a palladium-catalyzed coupling reaction of tributyl (3-methylbut-2-en-1-yl) stannane with 7-methoxy-8-iodocoumarin (8), which was from 7-hydroxy-8-iodocoumarin (7), to synthesize compound 1 [110].

The use of a microwave-promoted tandem Claisen rearrangement/olefin/cyclization method was an efficient approach for the synthesis of compound 1. As shown in Scheme 2, Konrádová et al. prepared compound 1 from an aldehyde synthon (9) by substitution and reduction reactions at a 78% yield [111]. Schmidt et al. obtained compound 11 straight from compound 9 by substitution reaction, skipping the reduction step from compound 10 to compound 11, and the yield of compound 1 was 59% [112]. Bromination or iodination of 2-hydroxy-4-methoxybenzaldehyde (9) with Br₂ or NIS in the presence of aluminum chloride produced compounds 12a and 12b. These compounds were then reacted with the Wittig reagent to provide compounds 13a and 13b. The C-H activation/cyclization of compounds 13a and 13b was catalyzed by rhodium (III) to give coumarins 14a and 14b, respectively. Finally, compound 1 was synthesized from compound 14a by Stille cross-coupling reaction [113]. Compared to palladium and nickel reagents, Grignard reagents align better with sustainable development principles. They can be modified into highly active derivatives by incorporating inexpensive and environmentally friendly transition metals, such as iron, zinc, and copper. Liu et al. therefore employed a non-precious metal-assisted Grignard reagent (using CuI and LiCl as promoters) to synthesize compound 1 from compound 14b at an 80% yield. [7].

As shown in Scheme 3, a series of oxime derivatives of (E)-4-chloro-2-oxo-2H-chromene-3-carbaldehyde (19a–19z and 19a’–19d’) were prepared through the successive three-step reactions from 2-hydroxyacetophenones (15a–15e) [114]. Among them, target compounds 19a (EC₅₀: 8.06 µg/mL), 19g (EC₅₀: 4.75 µg/mL), and 19n (EC₅₀: 5.43 µg/mL) showed a slightly lower inhibitory effect against Botrytis cinerea than boscalid (EC₅₀: 0.88 µg/mL). In addition, the majority of compounds exhibited similar inhibitory effectiveness to boscalid against Alternaria solani; in particular, compounds 19c (EC₅₀: 5.39 µg/mL) and 19g (EC₅₀: 5.80 µg/mL) showed greater inhibitory effects than boscalid (EC₅₀: 13.60 µg/mL). Against Alternaria alternata, compound 19g (EC₅₀: 5.74 µg/mL) displayed comparable inhibitory activity to boscalid (EC₅₀: 2.55 µg/mL).

As shown in Scheme 4, Ma et al. developed a series of coumarin derivatives using ring-merging and ring-opening strategies [115]. The intermediates 20–22 were synthesized in multistep reactions using 2,4-dihydroxybenzaldehyde (2) as the raw material. The treatment of compound 20 with the corresponding bromides provided compounds 23a–23c. Acylation of 20–22 gave derivatives 24a–24d, 25a–25c, and 26a–26e. Compound 24a (EC₅₀: 1.56 µg/mL) showed high inhibitory activity against Pyricularia grisea, which was more than 3 times more potent than chlorothalonil (EC₅₀: 5.81 µg/mL). Compound 24a showed good lethal activity against Ostrinia nubilalis, and its fatality rate was 67%, which was similar to that of matrine.

As shown in Scheme 5, a highly effective microwave-promoted technique was created for the synthesis of a number of pyrano [3,2-c]chromene-2,5-diones (28a–28o) and furo [3,2-c]coumarins (29(a–d)–33(a–d)) [116,117]. Among them, compounds 30c, 32b, 32c, and 33b showed high inhibitory activity against B. cinerea, Colletotrichum capsica, and Rhizoctorzia solani. In particular, compound 30c was more effective than azoxystrobin (EC₅₀: 0.158 µM) against B. cinerea (EC₅₀: 0.110 µM) and C. capsica (EC₅₀: 0.040 µM), making it the most promising choice. Additionally, compound 33b (EC₅₀: 0.051 µM) was equally as effective as the control azoxystrobin (EC₅₀: 0.053 µM) against R. solani. As shown in Scheme 6, two series of 7-pyrazolecoumarins (36a–36p) and 7-pyrrolecoumarins (38a–38h) were synthesized from m-aminophenol (34) via the intermediates 35a–35h and 37 [118]. In particular, compounds 36g, 38a–d, and 38h showed good antifungal efficacy against Cucumber anthrax and Alternaria leaf spot, which was superior to the control osthole. Compared to osthole (EC₅₀: 67.2 µg/mL), compound 36g exhibited a greater inhibitory effect against R. solani (EC₅₀: 15.4 µg/mL).

4. Structural Modifications of Osthole and Its Derivatives

Structural modifications of osthole at different positions are outlined in Figure 3.

4.1. Structural Modifications on the Lactone Ring of Osthole

One of the key methods for finding novel insecticides is the structural modification of natural products (NPs). By opening the lactone of osthole (1), Xu et al. produced two series of amide/ester derivatives of osthole [95]. As seen in Scheme 7, compounds 41b, 41l, 42l, 42m, 44h, 44l, and 44m showed more pronounced growth inhibition against M. separata than the precursor osthole, with corrected final mortality rates (CFMRs) of 62.0–68.9% at 1 mg/mL. The acaricidal activity of compounds 41b (LC₅₀: 0.238 mg/mL), 41i (LC₅₀: 0.226 mg/mL), and 42m (LC₅₀: 0.205 mg/mL) against T. cinnabarinus was 5.7–6.6 times higher than that of osthole (LC₅₀: 1.359 mg/mL); thus, compounds 41b and 42m have potential for further development as pesticides.

As shown in Scheme 8, a series of novel osthole-type ester derivatives (47a–47z) was prepared by modifying the osthole lactone ring [119]. Among them, compounds 47c (LC₅₀: 0.31 mg/mL), 47d (LC₅₀: 0.24 mg/mL), and 47e (LC₅₀: 0.28 mg/mL) showed strong acaricidal activity against T. cinnabarinus, as well as high control efficiency. In particular, compound 47d had more than five times the acaricidal activity of precursor 1 (LC₅₀: 1.22 mg/mL), and compounds 47i, 47n, and 47o had 1.6–1.8 times the insecticidal activity against M. separata compared to 1. Scheme 9 illustrates how N-hydroxyamide 51 was made by hydrolyzing 1 [120]. Compound 51 inhibited angiogenesis and suppressed tumor cell proliferation by targeting VEGFR2 signaling. In addition, HDAC6-induced Hsp90 hyperacetylation, and HDAC6-enhanced cyclin D1 and CDK4 degradation may be mediated by N-hydroxyamide 52-induced G1 growth arrest [121].

4.2. Structural Modifications at the C-7 Position of Osthole

As depicted in Scheme 10, Zhou et al. prepared a series of osthole derivatives and tested their anti-inflammatory properties [42]. The majority of them were able to successfully suppress the release of inflammatory cytokines, including IL-6 in mouse macrophages J774A activated by LPS. Compound 56m (IC₅₀: 4.57 μM) showed the strongest in vitro anti-inflammatory activity, which was 32 times higher than that of osthole. Compound 56m significantly reduced DSS-induced ulcerative colitis and LPS-induced acute lung damage, and it is a potential anti-inflammatory candidate. As described in Scheme 11, Zhang et al. used an MTT assay to evaluate the cytoprotective ability of osthole-based compounds [122]. At 10 μM, compound 59c demonstrated significant neuroprotective efficacy against H₂O₂ (45.7 ± 5.5%), oxygen glucose deprivation (64.6 ± 4.8%), and Aβ₄₂ (61.4 ± 5.2%).

The ability of compound 60c (50.4 ± 7.1%) to suppress NO has outperformed that of the positive medication indomethacin. The neuroprotective effect of osthole may be improved by the addition of piperazine, tetrahydropyrrole, and aromatic amine groups.

4.3. Structural Modifications at the C-8 Position of Osthole

The carboxylic acid ester scaffold, as a potent pharmacophore, is widely utilized in structural modification strategies [123]. As depicted in Scheme 12, Hao et al. designed and synthesized a series of osthole ester derivatives (66a–66y) and evaluated their agricultural bioactivities [124]. Compound 66n exhibited significant insecticidal activity against M. separata as compared to that of precursor 1. Compounds 66i and 66j demonstrated 2.6 and 3.3 times the acaricidal activity of 1, and good control effects in the glasshouse. As shown in Scheme 13, Hao et al. prepared two series of novel ester and amide derivatives modifying the C-4′ position of osthole (68a–68w and 69a–69j) [125]. Compounds 68b (LC₅₀: 0.492 mg/mL) and 68e (LC₅₀: 0.509 mg/mL) showed 3.2 and 3.1 times more acaricidal activity than 1 (LC₅₀: 1.578 mg/mL) against T. cinnabarinus, and the aphidicidal activities of compounds 68w (LC₅₀: 0.039 mg/mL), 69f (LC₅₀: 0.034 mg/mL), and 69g (LC₅₀: 0.038 mg/mL) against Aphis citricola were 1.9–2.1 times that of 1 (LC₅₀: 0.073 mg/mL).

As shown in Scheme 14, Ren et al. regioselectively semi-prepared series of novel derivatives (70a–70s) containing hydrazone/acylhydrazone/sulfonylhydrazone skeletons at the C-8 position of osthole [126]. Benzoylhydrazone 70b demonstrated 1.6 times the insecticidal activity of 1 against M. separata. The insecticidal activity can be enhanced by adding acylhydrazones to the 3′-methyl-2′-butylenyl fragment at the C-8 position of the osthole. As shown in Scheme 15, a number of osthole-based N-hydroxycinnamates (71–79) were prepared and examined for their ability to inhibit enzymes [127]. Comparable to that of suberoylanilide hydroxamic acid (SAHA; IC₅₀: 24.5 nM), compounds 74d (IC₅₀: 24.5 nM), 74e (IC₅₀: 20.0 nM), and 74g (IC₅₀: 19.6 nM) showed good inhibitory effects against nuclear HDACs in HeLa cells. Furthermore, three different kinds of osthole derivatives were combined with SAHA-like hydroxamates. Compounds 78c, 78d, and 78c had greater anti-HDAC-8 efficacy in addition to SAHA-like activity against HDAC-1, HDAC-4, and HDAC-6 [128].

A series of oxime ester derivatives of osthole (81a–81z, Scheme 16) were synthesized by selectively oxidizing 1 in the presence of selenium dioxide [129]. The acaricidal activity of compound 81c (LC₅₀: 0.316 mg/mL) against T. cinnabarinus was more than three times that of its precursor 1 (LC₅₀: 1.011 mg/mL), and it was particularly effective in the greenhouse. Among them, compounds 81c and 81f had the strongest acaricidal activity against M. separata, with final mortality rates of 70.4% and 70.4%, respectively. Scheme 17 illustrated the construction of novel osthole esters (83a–83s) containing the isoxazoline fragment [130]. Compounds 82 (LC₅₀: 0.75 mg/mL) and 83h (LC₅₀: 0.76 mg/mL) showed more than 1.5 times the acaricidal activity against T. cinnabarinus than 1 (LC₅₀: 1.14 mg/mL), and also had good control in the greenhouse. At 1 mg/mL, compounds 83a (FMR: 55.1%), 83c (FMR: 62.0%), and 83o (FMR: 55.1%) showed 1.5–1.6 times the growth inhibition against M. separata compared to 1. The addition of the acryloyloxy group to the C-4′ position of osthole was critical for insecticidal and acaricidal properties. As shown in Scheme 18, the new dihydropyrimidinone analog of osthole (84) was synthesized by the Biginelli reaction [131]. Compound 84 exhibited potent inhibitory effects on colon (Colo-205), prostate (PC-3), leukemia (THP-1), and lung (A549) cancer cell lines, as well as on normal cell line fR-2, with IC₅₀ values of 37.6, 40.8, 65.8, 67.8, and 68.8 µM, respectively.

4.4. Structural Modifications at the C-7 and C-8 Positions and on the Lactone Ring of Osthole

As described in Scheme 19, a series of new 2-isopropanol-4-methoxy-7-alkyl/aryloxycarbonyl-(E)-vinyl-2,3-dihydrobenzofuran derivatives (87a–87z and 87a’–87h’) were designed and synthesized. Among all derivatives, compound 87b’ exhibited promising insecticidal activity against P. xylostella with an LC₅₀ value of 0.759 mg/mL, which was higher than that of 1 (LC₅₀: 1.415 mg/mL). Additionally, compound 87e’ displayed 3.3 times higher acaricidal activity and good control effects compared to those of 1 [94]. As shown in Scheme 20, Ren et al. used osthole as raw material to prepare a series of new acrylate derivatives (90a–90z and 90a’–90m’) of isopropene-2,3-dihydrobenzofuran via consecutive bromination, rearrangement, and esterization processes [96]. Among them, the insecticidal activity of compound 90d’ (LC₅₀: 0.368 mg/mL) against P. xylostella was 3.5 times greater than that of 1 (LC₅₀: 1.281 mg/mL). The acaricidal activity of compound 90l’ (LC₅₀: 0.165 mg/mL) was 8.3 times higher than that of 1 (LC₅₀: 1.367 mg/mL) against T. cinnabarinus, and it could be further developed as an acaricide. As illustrated in Scheme 21, You et al. synthesized a series of 3-aryl-substituted derivatives (92a–92j) by structural modification at the C-7 and C-8 positions and on the lactone ring of osthole [132]. Some derivatives showed good inhibitory effects, among which compound 92e inhibited MCF-7 and MDA-MB-231, with IC₅₀ values of 0.24 and 0.31 µM, respectively, surpassing the parent compound osthole by over 100 times. The 7-methoxy and 3-aryl ring were critical for preserving cytotoxicity potency.

5. Structure–Activity Relationships of Osthole and Its Derivatives

As described in Figure 4, the structure–activity relationships (SARs) of osthole and its derivatives can be generally summarized as follows: (i) the introduction of an aromatic ring at the C-3 position of osthole can improve anticancer activity [120,121]. Incorporating heterocyclic fused fragments at the C-3 and C-4 positions resulted in derivatives showing good antifungal activity [116,117]. Opening the lactone ring and introducing aliphatic chain ester or amide groups were necessary for the insecticidal activity [94,95,119]. Additionally, the introduction of an N-hydroxylamide group can also augment anticancer activity [120,121]. (ii) The introduction of the pyrrole/pyrazole group at the C-7 position was necessary for the antifungal activity [118]. Adding the N-hydroxycinnamate group can also improve the anticancer activity [127]. Moreover, the introduction of AMP mimics, flexible carbon chains, and amide groups were beneficial for anti-inflammatory activity [42]. (iii) The isopentenyl fragment underwent oxidation and was subsequently converted into ester derivatives that exhibited inhibitory activity against acetylcholinesterase [62,124]. In particular, the introduction of N-benzoylthioureas/isoxazolines, hydrazones/acylhydrazones/sulfonylhydrazones, oxime esters, amides, and carboxylate esters groups were important for the pesticidal activity [125,126,131].

6. Conclusions

Recent advances in the biological activities, total synthesis, and structural modification of osthole and its derivatives were reviewed in the present work. Furthermore, the mechanisms of action and structure–activity relationships (SARs) of osthole and its derivatives were summarized. To find more pronounced compounds, extensive structural modification of osthole and its derivatives should be performed, and the scope of bioactivities can be broadened. With ongoing in-depth research on osthole and its derivatives, it is anticipated that the development of more osthole-type products will promote their practical applications in medicinal and agricultural fields, thereby contributing to human health and sustainable agricultural development.