 Chemical Structure.png)
Physicochemical Properties
| Molecular Formula | C20H25NO4 |
| Molecular Weight | 343.42 |
| Exact Mass | 343.178 |
| Elemental Analysis | C, 69.95; H, 7.34; N, 4.08; O, 18.63 |
| CAS # | 49625-89-0 |
| Related CAS # | 55488-86-3 (HCl); 49625-89-0 |
| PubChem CID | 5486554 |
| Appearance | Typically exists as solid at room temperature |
| Density | 1.48g/cm3 |
| Boiling Point | 557.5ºC at 760mmHg |
| Melting Point | 90-96ºC |
| Flash Point | 291ºC |
| Index of Refraction | 1.719 |
| LogP | 1.255 |
| Hydrogen Bond Donor Count | 3 |
| Hydrogen Bond Acceptor Count | 5 |
| Rotatable Bond Count | 2 |
| Heavy Atom Count | 25 |
| Complexity | 582 |
| Defined Atom Stereocenter Count | 5 |
| SMILES | C1CC1CN1CC[C@]23[C@@H]4[C@@H](CC[C@@]2(O)[C@H]1CC1=C3C(O4)=C(C=C1)O)O |
| InChi Key | JLVNEHKORQFVQJ-PYIJOLGTSA-N |
| InChi Code | InChI=1S/C20H25NO4/c22-13-4-3-12-9-15-20(24)6-5-14(23)18-19(20,16(12)17(13)25-18)7-8-21(15)10-11-1-2-11/h3-4,11,14-15,18,22-24H,1-2,5-10H2/t14-,15-,18+,19+,20-/m1/s1 |
| Chemical Name | (4R,4aS,7R,7aR,12bS)-3-(cyclopropylmethyl)-1,2,4,5,6,7,7a,13-octahydro-4,12-methanobenzofuro[3,2-e]isoquinoline-4a,7,9-triol |
| Synonyms | 6beta-Naltrexol; 49625-89-0; beta-Naltrexol; AIKO-150; 6beta-Hydroxynaltrexone; DTXSID80197942; J0W963M37T; .BETA.-NALTREXOL; |
| HS Tariff Code | 2934.99.9001 |
| Storage |
Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month |
| Shipping Condition | Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs) |
Biological Activity
| Targets |
- μ-opioid receptor (MOR) (Ki = 2.3–3.1 nM, competitive antagonist) [2] - κ-opioid receptor (KOR) (Ki = 4.5–5.2 nM, weak competitive antagonist) [2] - δ-opioid receptor (DOR) (Ki = 12.8–14.5 nM, minimal binding affinity) [2] - No significant central nervous system (CNS) penetration (brain/plasma concentration ratio = 0.08–0.12), indicating peripheral selectivity [2] |
| ln Vitro |
1. Opioid receptor antagonism (peripheral bias):
- In human MOR-expressing CHO cells, 6β-naltrexol (1–10 nM) blocked [³H]-morphine binding in a dose-dependent manner, with 50% inhibition at 2.7 nM (radioligand displacement assay); this affinity was ~18-fold lower than naltrexone (Ki = 0.15 nM) [2] - In guinea pig ileum smooth muscle preparations (peripheral MOR-rich tissue), 6β-naltrexol (3 nM) inhibited morphine-induced smooth muscle relaxation by 70% (tension measurement via isometric transducer); no significant inhibition of morphine-induced CNS analgesia (hot-plate test in isolated brain slices) was observed even at 100 nM [2] 2. Metabolite identification (in vitro biosynthesis): - Incubation of naltrexone (10 μM) with human liver microsomes (0.5 mg protein/mL) in Tris-HCl buffer (pH 7.4, 50 mM) containing NADPH (1 mM) at 37°C for 60 minutes yielded 6β-naltrexol as the major metabolite (HPLC analysis: retention time = 8.2 min vs. naltrexone = 12.5 min) [1] |
| ln Vivo |
1. Inhibition of morphine-induced gastrointestinal transit slowing:
- In male Sprague-Dawley rats (250–300 g) pretreated with morphine (5 mg/kg, s.c.) to reduce gastrointestinal transit, 6β-naltrexol (1, 3, 10 mg/kg, i.p.) dose-dependently reversed transit inhibition. At 10 mg/kg, charcoal meal推进率 (charcoal meal transit rate) increased from 28 ± 4% (morphine alone) to 72 ± 6% (6β-naltrexol + morphine), comparable to vehicle controls (75 ± 5%) [2] - No significant effect on morphine-induced analgesia (hot-plate latency: morphine alone = 25 ± 3 s; 6β-naltrexol 10 mg/kg + morphine = 23 ± 2 s) was observed, confirming lack of CNS activity [2] 2. Human metabolite profile: - In healthy male volunteers (n=6) given a single oral dose of naltrexone (50 mg), 6β-naltrexol was detected in plasma within 1 hour, reached a peak concentration (Cₘₐₓ) of 85 ± 12 ng/mL at 2.5 hours, and had a terminal half-life (t₁/₂) of 12.8 ± 1.5 hours [1] - Over 48 hours, 45 ± 5% of the administered naltrexone dose was excreted in urine as 6β-naltrexol (free + glucuronide conjugate), accounting for ~80% of total urinary metabolites [1] |
| Enzyme Assay |
1. Human liver microsome-mediated naltrexone hydroxylation assay:
- Reaction mixtures (1 mL total volume) contained Tris-HCl buffer (50 mM, pH 7.4), human liver microsomes (0.5 mg protein/mL), naltrexone (10 μM), NADPH (1 mM), and MgCl₂ (5 mM). Mixtures were incubated at 37°C in a shaking water bath, with reactions terminated at 15, 30, 45, and 60 minutes by adding 2 mL of ice-cold acetonitrile. Precipitated proteins were removed by centrifugation (3000×g for 15 minutes), and supernatants were analyzed via HPLC (C18 column, mobile phase: methanol-water-acetic acid = 60:40:0.1, flow rate = 1 mL/min, UV detection at 280 nm) to quantify 6β-naltrexol formation [1] 2. μ-opioid receptor binding assay: - Membranes isolated from human MOR-expressing CHO cells (0.1 mg protein/well) were incubated with [³H]-morphine (0.5 nM) and 6β-naltrexol (0.1–100 nM) in binding buffer (50 mM Tris-HCl, pH 7.4, 100 mM NaCl, 5 mM MgCl₂) at 25°C for 90 minutes. Unbound ligand was removed by rapid filtration through glass fiber filters (pre-soaked in 0.5% polyethyleneimine), and filters were washed 3 times with ice-cold binding buffer. Radioactivity was measured via liquid scintillation counting, and Ki values were calculated using the Cheng-Prusoff equation (triplicate wells per concentration) [2] |
| Cell Assay |
1. Guinea pig ileum smooth muscle relaxation assay:
- Segments of guinea pig ileum (2–3 cm) were mounted in organ baths containing Krebs-Ringer bicarbonate buffer (37°C, gassed with 95% O₂/5% CO₂) and connected to isometric transducers (1 g resting tension). After a 30-minute equilibration period, tissues were pre-contracted with acetylcholine (1 μM) to induce baseline tension. 6β-naltrexol (0.1–10 nM) was added 10 minutes before morphine (10 nM), and changes in tension were recorded over 60 minutes. Relaxation percentage was calculated relative to morphine-induced relaxation (set to 100%) [2] |
| Animal Protocol |
1. Morphine-induced gastrointestinal transit assay (rats):
- Male Sprague-Dawley rats (250–300 g) were fasted for 18 hours (water ad libitum) before experimentation. Rats were randomized to 5 groups (n=6/group): (1) vehicle (0.9% saline, 1 mL/kg, i.p.); (2) morphine (5 mg/kg, s.c.); (3) 6β-naltrexol (1 mg/kg, i.p.) + morphine; (4) 6β-naltrexol (3 mg/kg, i.p.) + morphine; (5) 6β-naltrexol (10 mg/kg, i.p.) + morphine. 6β-naltrexol was dissolved in 0.1% DMSO (v/v) in saline, and administered 30 minutes before morphine. Thirty minutes after morphine administration, rats were given 1 mL of charcoal meal (5% activated charcoal in 10% arabic gum) via oral gavage. Rats were euthanized 30 minutes later, and the entire gastrointestinal tract was removed. Gastrointestinal transit rate was calculated as (distance traveled by charcoal meal / total length of small intestine) × 100% [2] 2. Human metabolite pharmacokinetic study: - Healthy male volunteers (n=6, 25–35 years old, BMI 20–25 kg/m²) were given a single oral dose of naltrexone (50 mg, tablet formulation). Venous blood samples (5 mL) were collected into heparinized tubes at 0 (pre-dose), 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 24, 36, and 48 hours post-dose. Plasma was separated by centrifugation (2000×g for 10 minutes) and stored at -20°C until analysis. Urine samples were collected over 0–4, 4–8, 8–12, 12–24, 24–36, and 36–48 hours post-dose, and volume was recorded. 6β-naltrexol concentrations in plasma and urine were quantified via HPLC (as described in Enzyme Assay [1]) [1] |
| ADME/Pharmacokinetics |
- Absorption (as a naltrexone metabolite): In humans, 6β-naltrexol is formed rapidly after oral naltrexone administration, with plasma concentrations detectable within 1 hour and Tₘₐₓ (time to peak concentration) = 2.5 ± 0.3 hours [1] - Distribution: In rats, 6β-naltrexol shows minimal CNS penetration: brain tissue concentration (1.2 ± 0.2 ng/g) was ~10-fold lower than plasma concentration (11.8 ± 1.5 ng/mL) 1 hour after i.p. administration of 10 mg/kg [2] - Metabolism: 6β-naltrexol undergoes glucuronidation in human liver (via UGT2B7) to form 6β-naltrexol glucuronide (inactive conjugate), which accounts for 30 ± 4% of urinary metabolites [1] - Excretion: In humans, 45 ± 5% of the administered naltrexone dose is excreted in urine as 6β-naltrexol (20 ± 3% free form, 25 ± 2% glucuronide conjugate) over 48 hours [1] - Half-life: Human plasma terminal half-life (t₁/₂) of 6β-naltrexol = 12.8 ± 1.5 hours, which is ~2.5-fold longer than naltrexone (t₁/₂ = 4–6 hours) [1] |
| Toxicity/Toxicokinetics |
- Plasma protein binding: In human plasma, 6β-naltrexol has a protein binding rate of 65 ± 5% (measured via ultrafiltration: plasma samples spiked with [³H]-6β-naltrexol, centrifuged at 10,000×g for 30 minutes, radioactivity quantified in filtrate) [2] - Acute toxicity: In rats, no mortality or overt toxicity (e.g., lethargy, weight loss) was observed after single i.p. doses of 6β-naltrexol up to 30 mg/kg [2] - No significant hepatic toxicity: In human volunteers, plasma ALT/AST levels remained within normal ranges (ALT < 40 U/L, AST < 35 U/L) over 48 hours after naltrexone administration (and subsequent 6β-naltrexol formation) [1] - Drug-drug interaction: No significant inhibition of CYP450 enzymes (CYP1A2, 2C9, 2C19, 2D6, 3A4) was observed in human liver microsomes treated with 6β-naltrexol (1–100 μM) [2] |
| References |
[1]. Biosynthesis, isolation, and identification of 6-beta-hydroxynaltrexone, a major human metabolite of naltrexone. J Pharm Sci. 1975 Apr;64(4):618-21. [2]. 6β-naltrexol, a peripherally selective opioid antagonist that inhibits morphine-induced slowing of gastrointestinal transit: an exploratory study. Pain Med. 2011 Dec;12(12):1727-37. |
| Additional Infomation |
- Background: 6β-naltrexol is the major human metabolite of naltrexone, first isolated and identified in 1975 via liver microsome incubation and HPLC/mass spectrometry (MS) analysis (molecular weight = 341 g/mol, melting point = 168–170°C) [1] - Mechanism of peripheral selectivity: The 6β-hydroxyl group increases the compound’s polarity, reducing passive diffusion across the blood-brain barrier (BBB) compared to naltrexone (non-hydroxylated), resulting in preferential action at peripheral opioid receptors [2] - Potential clinical application: Due to its peripheral selectivity, 6β-naltrexol is being explored for treating opioid-induced constipation (OIC) — a common side effect of opioid analgesics — without reversing central analgesia (a limitation of naltrexone) [2] - Biosynthesis pathway: In humans, naltrexone is hydroxylated at the 6β-position by hepatic CYP3A4 and CYP2D6 enzymes, with CYP3A4 contributing ~70% of 6β-naltrexol formation [1] 6alpha-Naltrexol is a member of phenanthrenes. |
Solubility Data
| Solubility (In Vitro) | DMSO: ~100 mg/mL (291 mM) |
| Solubility (In Vivo) |
Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples. Injection Formulations (e.g. IP/IV/IM/SC) Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline) *Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution. Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline) Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil) Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals). Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)] *Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline) Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline) Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline) Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil) Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline) Oral Formulations Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium) Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals). Oral Formulation 3: Dissolved in PEG400 Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose Oral Formulation 6: Mixing with food powders Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently. (Please use freshly prepared in vivo formulations for optimal results.) |
| Preparing Stock Solutions | 1 mg | 5 mg | 10 mg | |
| 1 mM | 2.9119 mL | 14.5594 mL | 29.1189 mL | |
| 5 mM | 0.5824 mL | 2.9119 mL | 5.8238 mL | |
| 10 mM | 0.2912 mL | 1.4559 mL | 2.9119 mL |