Ingredients5-Alpha-furost-20(22)-en-12-one-3β,26-diol is the steroidal aglycone core that defines a structurally important subclass of furostanol saponins isolated from several medicinal plants. In the scientific literature it is commonly encountered not in its free (aglycone) form but as the aglycon backbone of glycosylated saponins — most notably the compound class found in Tribulus terrestris L. fruits and Trigonella foenum-graecum (fenugreek) seeds. It belongs to the furostane skeleton of steroidal saponins, characterized by a bicyclic furanoid ring system in the side chain, the presence of a Δ20(22) double bond, a 12-oxo (keto) group, and hydroxyl substituents at C-3β and C-26.
A furostanol glycoside bearing this exact aglycone was isolated from the fruits of Tribulus terrestris L., with its structure established as 26-O-β-D-glucopyranosyl-(25S)-5α-furostane-20(22)-en-12-one-3β,26-diol-3-O-α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→4)]-β-D-galactopyranoside, on the basis of 1D and 2D-NMR techniques including COSY, HMBC, and HMQC correlations. This structure, sharing the same aglycone moiety, has also been identified in compounds named in the series "terrestrosin F–K" and in furostanol saponins from fenugreek seeds bearing the trivial names trigoneosides and Fenfuro-related saponins.
The assignments of the aglycone moiety of these saponins were determined by DEPT, HMQC, HMBC spectroscopy, and comparison with tribufuroside C, confirming the aglycone as 5α-furost-20(22)-en-12-one-3β,26-triol — the free, un-glucosylated form closely related to the 26-diol. When the 26-hydroxyl bears a glucosyl residue (as in all naturally occurring glycoside forms), the compound is typically referred to by the full glycoside name, with the 3β,26-diol designation referring to the pattern of substitution on the aglycone scaffold.
Steroidal saponins isolated from T. terrestris are spirostanol saponins bearing a sugar chain linked to C-3, and furostanols carrying a sugar chain at C-3 and a D-glucose residue at C-26. The 5α-furost-20(22)-en-12-one-3β,26-diol aglycone thus represents the deglycosylated core of an important family of bioactive furostanol saponins found across several genera.
The fruits of Tribulus terrestris contain important secondary metabolites such as saponins, polyphenolic compounds, and alkaloids; the steroidal saponins are mainly furostanol and spirostanol type.
Spirostanol and furostanol saponins are considered the most characteristic chemicals in T. terrestris; to date many kinds of steroidal saponins have been isolated from it, including 58 kinds of spirostane saponins and 50 kinds of furostane saponins.
Beyond Tribulus terrestris, furostanol saponins sharing the 5α-furost-20(22)-en-12-one-3β,26-diol aglycone (or its close structural variants) have been reported in:
Studies have revealed that the saponin composition in Tribulus terrestris is strictly linked with the origin of the plant and climatic conditions; geographical regions significantly influence the composition of herbal drugs. For example, prototribestin was detected only in samples collected from Bulgaria, Turkey, Greece, Macedonia, Iran, and Serbia, and appeared to be a marker for the European variety.
The 5α-furost-20(22)-en-12-one-3β,26-diol aglycone is closely related to, but distinct from, the aglycone of protodioscin, which is one of the most intensively studied furostanol saponins. Protodioscin (26-O-β-D-glycopyranosyl-22-hydroxyfurost-5-ene-3β,26-diol-3-O-β-diglucorhamnoside) belongs to the furostanol class of saponins, having a molecular weight of 1049.2 g mol⁻¹. The key differences are the presence of a C-12 ketone and the Δ20(22) double bond in the 5α-furost-20(22)-en-12-one-3β,26-diol scaffold, versus the C-12 hydroxyl and the Δ5(6) double bond in the protodioscin scaffold. Both belong to the furostanol saponin family and have been isolated from the same plant species.
The extract obtained from the aerial parts of Tribulus terrestris contains furostanol-type steroidal glycosides (saponins), of which the predominant active component is protodioscin (PTN), which represents 45% of the extract. Saponins bearing the 5α-furost-20(22)-en-12-one-3β,26-diol aglycone are found alongside protodioscin as co-occurring minor constituents.
Many pharmaceutical preparations and food supplements with steroidal saponins from Tribulus terrestris and related plants as the active compounds have been commercially available. These are typically marketed as:
Tribulus terrestris L. is an annual plant found around the world; its fruits have been used in traditional Chinese medicine for treatment of eye problems, edema, abdominal distention, emission, morbid leucorrhea, sexual dysfunction, and veiling. It has also been used as a medicine in India, South Africa, and Japan.
The plant is a perennial widely distributed in subtropical areas; its dried fruit, named "Jili" in Chinese, has been used as a TCM for the treatment of edema, abdominal distention, emission, morbid leucorrhea, and vitiligo. Additionally, it has been used as an aphrodisiac tonic and antibacterial agent, and for the treatment of cardiovascular diseases.
Asparagus cochinchinensis, known as "Tianmendong" in China, has had its roots used in Chinese folk medicine for the treatment of cough, acute and chronic bronchitis, chronic pharyngitis, hemorrhoids, and tumors for thousands of years.
Since ancient times, Tribulus terrestris has been used in Indian and Chinese traditional medicine to treat hypertension, premature ejaculation, erectile dysfunction, vitiligo, and kidney and eye problems. It has anti-urolithiatic, diuretic, antiacetylcholine, and aphrodisiac properties and has been used to stimulate spermatogenesis and libido.
In both Ayurvedic and Chinese medicine, fenugreek leaves and seeds have long been known for therapeutic efficacy in diabetes, muscle building, and wrestling. This traditional use of fenugreek, driven in part by its furostanol saponin content, forms an ancient foundation for modern investigation into its metabolic and androgenic properties.
Ancient Ayurvedic and Traditional Chinese Medicine (TCM) texts mention the use of furostanol-rich herbs for enhancing vitality, supporting reproductive health, and promoting general well-being. For example, fenugreek seeds, abundant in furostanol saponins, have been utilized to support lactation, improve digestion, and manage blood sugar levels.
When isolated from plant sources, the 5α-furost-20(22)-en-12-one-3β,26-diol scaffold occurs as a glycoside, i.e., with sugar chains attached at C-3 and C-26. The saponins bearing this aglycone are part of a broader phytochemical profile that includes:
Among the total phytochemical constituents of Tribulus terrestris, the plant is composed of saponins, flavonoids, glycosides, alkaloids, and tannins. The steroidal saponins, such as protodioscin and protogracillin, are thought to confer to T. terrestris unique biological activities.
Within fenugreek seeds, bioactive constituents include fiber, 4-hydroxyisoleucine, steroidal saponins, protodioscin, glycosides, alkaloids, polyphenols, flavonoids, antioxidants, lipids, carbohydrates, amino acids, and hydrocarbons.
Further studies on the constituents of the fruits of Tribulus terrestris led to the isolation of six new furostanol saponins including 26-O-β-D-glucopyranosyl-(D-galactopyranosyl(1-2)-β-D-glucopyranosyl(1-4)-β-D-galactopyranoside bearing the furost-20(22)-en-12-one-3β,26-diol core, named terrestrosin F–K.
Steroid saponins, whose aglycones are usually a spirostanol or its derivatives, are commonly found in roots, tubers, leaves, blooms, or seeds in more than 100 families of plants. The strong foam-forming property in aqueous solution of steroidal saponins is their main feature. Previous research has revealed steroidal saponins possess various pharmacological activities, such as antifungal, hypocholesterolemic, antimitotic, and cAMP phosphodiesterase inhibitory effects.
It was proposed that the active components of T. terrestris can be converted enzymatically to weak androgens similar to dehydroepiandrosterone (DHEA), which could, in turn, be converted to more powerful androgens such as testosterone in the gonads and peripheral tissues.
Fenugreek's saponins, particularly protodioscin and furostanol glycosides, may support endogenous testosterone production by influencing steroidogenesis and modulating key enzymes like aromatase and 5-alpha reductase. It is important to note that these proposed mechanisms remain incompletely validated in rigorously controlled human studies.
Steroidal saponins may be responsible for intrinsic hormonal activity by directly stimulating responsive endocrine tissues such as the uterus and vagina.
Animal model data have suggested that Tribulus terrestris may act on testicular Leydig cells: histological and histochemical studies in mature male mice given Tribulus terrestris at 2 mg/kg body weight for 14 days demonstrated a considerable increase in the number of spermatocytes, spermatids, and sperms in parallel with an increase in the number of interstitial (Leydig) cells; T. terrestris was concluded to increase the number of Leydig cells, and the androgens produced by these cells are directly responsible for enhanced spermatogenesis. These are animal data and do not establish an equivalent effect in humans.
The favorable effects of fenugreek in diabetes are attributed to four bioactive components, including furostanol saponins, 4-hydroxyisoleucine, diosgenin, and fiber, which could improve insulin signaling by reducing oxidative stress and inflammation. Saponins and polyphenols available in fenugreek may also reduce hepatic gluconeogenesis based on preclinical studies.
Diosgenin and saponin are known to reduce fat by inhibiting cholesterol absorption, increasing biliary cholesterol secretion, and fecal excretion of neutral sterols, thus reducing liver cholesterol concentrations. Diosgenin also helps to improve glucose metabolism by promoting adipocyte differentiation and inhibiting inflammation in adipose tissues.
A large number of publications have revealed that steroid saponins share different cytotoxic properties that promoted their potential as anti-cancer drugs or adjuvants. Saponins in general can disrupt cell membrane integrity through interactions with membrane cholesterol, leading to cell lysis — a mechanism relevant to both cytotoxic and hemolytic activity. Furostanol saponins isolated from Tribulus terrestris fruits were evaluated for their inhibitory effects on tumour cells, and compounds bearing the 5α-furost-20(22)-en-3β,26-diol core showed potential anti-tumour activity.
Saponins have several important biological functions; they have been demonstrated to possess anti-inflammatory effects through the activation of macrophages and other immune cells, thereby modulating the immune system.
The most clinically investigated application of furostanol saponin-standardized extracts is male sexual dysfunction.
Key RCT (Kamenov et al., 2017): A Phase IV, prospective, randomized, double-blind, placebo-controlled clinical trial in parallel groups included 180 males aged 18–65 years with mild or moderate erectile dysfunction (ED) and with or without hypoactive sexual desire disorder (HSDD); 90 were randomized to T. terrestris and 90 to placebo. Patients with ED and hypertension, diabetes mellitus, and metabolic syndrome were included. Each tablet contained 250 mg dry extract standardized to furostanol saponins (not less than 112.5 mg); each patient received 3×2 film-coated tablets daily after meals for 12 weeks. Sexual function was assessed monthly by the International Index of Erectile Function (IIEF) Questionnaire and Global Efficacy Question (GEQ). Patients affected by mild to moderate ED and/or low libido may significantly benefit from oral therapy with T. terrestris, without any significant changes in biochemistry laboratory test results. The authors explicitly cautioned that based on the origin of the herbal medicine used in this study and the fact that this preparation is standardized with respect to furostanol saponins (calculated against protodioscin), the results of this trial should not be extrapolated directly to other T. terrestris preparations obtained from other regions.
Evidence strength: This single well-designed RCT provides moderate-quality evidence for a population with mild-to-moderate ED using a geographically specific Bulgarian preparation. The inability to directly attribute effect to the 5α-furost-20(22)-en-12-one-3β,26-diol scaffold specifically (as opposed to the full saponin mixture including protodioscin) is a limitation.
Despite proposed effects of T. terrestris supplementation as a testosterone booster through different mechanisms, 80% of the studies analyzed in a systematic review did not report significant changes in the androgen profile following T. terrestris supplementation (400–750 mg/d for 2–3 months).
Only two studies exclusively enrolled subjects with low testosterone levels (<350 ng/mL) and observed effects of T. terrestris supplementation as a testosterone booster. In both studies, subjects received 3 capsules daily (750 mg) of T. terrestris (Bulgarian origin, 250 mg per capsule with a minimum of 45% saponins) over 3 months. In one randomized, single-blind, placebo-controlled trial, 70 patients with late-onset hypogonadism reported approximately a 58 ng/mL (27%) increase in mean total testosterone levels (from ~215 to ~273 ng/dL, p < 0.001) in the group receiving T. terrestris.
Evidence strength: Evidence is mixed and limited. Effects on testosterone appear most pronounced in men with baseline androgen deficiency. Evidence in eugonadal healthy men or athletes is largely negative. The collective data do not robustly support a general testosterone-boosting effect.
An open-label, one-arm, single-center longitudinal study (Furosap® trial) examined the safety and efficacy on free and total testosterone levels, fasting blood sugar, blood pressure, sperm count, motility and morphology, DHEA-S, sexual health, reflex erection, mood alleviation, mental alertness, and total blood chemistry analyses over a period of 12 weeks in healthy male volunteers. This one-arm, open-labelled, multi-center study was conducted in 50 male volunteers (age 35–65 years) over 12 weeks to determine the efficacy of Furosap™ (500 mg/day/subject) on free and total testosterone levels, sperm profile, sperm morphology, libido and sexual health, mood and mental alertness, and broad spectrum safety parameters.
Sperm morphology improved in 14.6% of volunteers; the majority of subjects enrolled in the study demonstrated improvements in mental alertness and mood. Furthermore, cardiovascular health and libido were significantly improved.
Evidence strength: This was an uncontrolled, unblinded study without a placebo arm. Results must be interpreted cautiously and cannot establish causality. Absence of a control group is a critical limitation.
A multicenter, randomized, placebo-controlled, double-blind clinical study designed as add-on therapy evaluated Fenfuro (a standardized T. foenum-graecum seed extract enriched in approximately 40% furostanolic saponins, dose: 500 mg bid) or placebo given in addition to standard anti-diabetic therapy (metformin) in 154 male and female subjects (age: 25–60 years) with T2D over a period of 3 months.
Fenfuro caused significant reduction in both fasting plasma and post-prandial blood sugar levels. Approximately 83% of subjects reported decreases in fasting plasma sugar levels in the Fenfuro-treated group compared to 62% in the placebo group; 89% of subjects demonstrated reduction in post-prandial plasma sugar levels compared to 72% in the placebo group. HbA1c levels were reduced in both groups; the decrease in HbA1c levels was significant in both groups compared to respective baseline values. A significant increase in fasting and post-prandial C-peptide levels was observed compared to baseline values, while no significant changes in C-peptide levels were observed between the two groups. No significant adverse effects were observed by blood chemistry analyses.
The antihyperglycemic potential of a fenugreek seed extract with >45% furostanolic saponins was investigated in a randomized double-blind placebo-controlled trial; administration of a daily dosage of 500 mg × 2 for 12 weeks resulted in significant decrease in fasting and post-prandial glucose as well as glycated hemoglobin.
Evidence strength: The glycemic evidence for furostanol-rich fenugreek extracts is supported by at least two placebo-controlled RCTs in T2D patients, though both employed the extract as add-on to metformin, not as monotherapy. The multi-ingredient nature of the extract limits attribution of effects specifically to the furostanol saponins. Moderate-quality evidence for a supportive glycemic role in T2D in combination with standard therapy.
In a randomized, single-blind, placebo-controlled study of CrossFit® performance, two T. terrestris capsules from the Quamtrax laboratory were administered as a single dose of 770 mg daily on an empty stomach. Testosterone had no significant changes after the supplementation.
Evidence strength: Overall evidence for enhancement of athletic performance or body composition by furostanol saponin-standardized T. terrestris extracts in eugonadal athletes is weak and largely negative. The majority of controlled trials have not demonstrated significant effects on lean mass, strength, or hormonal parameters in healthy, normally androgenized individuals.
Results of human and animal clinical trials support a FSH-stimulating effect; in one study, 750 mg of active furostanol (TLSE) per day for 5 days was given to women and was shown to increase FSH and estradiol compared with baseline.
Evidence strength: Evidence for female sexual dysfunction is preliminary, with very limited clinical trial data. A systematic review of Tribulus terrestris for female sexual dysfunction was published (Martimbianco et al., 2020; PubMed PMID: 32736394), but the available trials were generally small and heterogeneous in design.
Preclinical studies indicate that tribulus has antihypertensive, anti-inflammatory, antiedematous, antioxidant, diuretic, hypoglycemic, antibacterial, antifungal, cardioprotective, and anticancer properties in laboratory settings. In one T2D clinical study, administration of fenugreek seed powder resulted in statistically significant reductions in total cholesterol, LDL-C, and triglycerides, along with a marked increase in HDL-C; these improvements are consistent with the hypolipidemic effects of fenugreek's bioactive compounds, particularly steroidal saponins and polyphenols, that modulate lipid metabolism.
Evidence strength: Cardiovascular benefits in humans remain mostly confined to lipid parameters in diabetic populations. Evidence is largely preclinical (animal and cell-based); human cardiovascular outcome data are absent.
Tribulus terrestris is known to possess many pharmacological properties, most notably anticancer activities, owing to its rich steroidal saponin contents; many reports are available elucidating the anticancer potential of these compounds. A large number of publications have revealed steroid saponins share different cytotoxic properties that promote their potential as anti-cancer drugs or adjuvants.
Evidence strength: All cytotoxic and anticancer evidence for furostanol saponins is preclinical — primarily in vitro cell line studies. No human clinical trials have evaluated anticancer efficacy of these specific compounds. This evidence does not support clinical anti-cancer applications at present.
The following dosages are reported directly from clinical studies and should be understood only within the context of the specific preparations studied:
Across these studies, oral doses of standardized furostanol saponin-containing extracts typically range from 500 mg to 1,500 mg per day of the extract. Duration in clinical trials ranged from 5 days to 12 weeks.
Extensive safety parameters evaluated in the Furosap™ study included blood chemistry data; no significant changes were observed in serum lipid function, cholesterol, triglyceride, HDL and LDL levels, hemogram (CBC), hepatotoxicity, or nephrotoxicity markers.
No significant adverse effects were observed by blood chemistry analyses in the Fenfuro multicenter RCT in T2D patients.
Transient gastrointestinal problems including irritation of gastric mucosa and gastric reflux, and nephrotoxicity, have been associated with consumption of tribulus. Consumption of tribulus causes motor neuron adverse effects in animals by affecting gamma-aminobutyric acid (GABA) receptors.
Severe hyperbilirubinemia was reported in a healthy 30-year-old male body-builder, followed by acute renal failure and bile-containing casts in the tubules associated with ingestion of tribulus extract tablets, once daily for "a few months."
Neuro-, hepatic, and renal toxicity suggestive of acute tubular necrosis was reported in a 28-year-old man who consumed large quantities of tribulus extract for its antiurolithiatic properties; he additionally developed hypertension, seizures, and markedly elevated serum aminotransferases (>40× upper limit of normal).
The steroidal saponin diosgenin, a related compound, is thought to be responsible for hepatotoxic effects associated with tribulus in reported cases. The evidence for direct hepatotoxicity from furostanol saponins specifically is primarily based on case reports rather than controlled studies.
Tribulus terrestris may cause gynecomastia in men, or excess body hair with loss of head hair; this may indicate that other steroidal saponins possess progesterone or estrogenic effects.
There are conflicting reports as to the androgenicity of the whole Tribulus extract. In Wistar rats, Tribulus terrestris did not stimulate endocrine-sensitive tissue such as circulating androgens, sperm production, prostate, seminal vesicle, uterus, or vagina, indicating lack of androgenic and estrogenic activity in vivo.
Tribulus terrestris should not be taken by breast or prostate cancer patients, patients with ulcers, stomach inflammation, or serious digestion or liver disorders based on preclinical toxicological observations and clinical case reports.
Given the potential glycemic effects documented in clinical trials with furostanol-standardized fenugreek extracts, concurrent use with anti-diabetic medications such as metformin may produce additive blood glucose-lowering effects. In the Fenfuro RCT, the supplement was administered on top of metformin therapy; any individual receiving both should be monitored for hypoglycemia, as implied by the design of those trials.
Phytochemical studies have shown great disparities in the content of active substances, in particular the concentration of furostanol and spirostanol saponosides, considered to be the predominant active ingredients, across preparations from different geographic sources. This variability means safety and efficacy data from one preparation cannot be uniformly extrapolated to others.
Health conditions that 5-alpha-furost-20(22)-en-12-one-3 beta, 26-diol may help support.
Body systems that 5-alpha-furost-20(22)-en-12-one-3 beta, 26-diol may help support.
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