OTR-AC (MK-2866 ESTER) SARM is sold for laboratory research use only. Terms of sale apply. Not for human consumption, nor medical, veterinary, or household uses. Please familiarize yourself with our Terms & Conditions prior to ordering.

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Molecular Formula C₂₁H₁₆F₃N₃O₄
Molecular Weight 431.37
Purity ≥99% Pure (LC-MS)
Storage Store in cool dry environment, away from direct sunlight.
Terms Lab Use Only. This information is for educational purposes only and does not constitute medical advice.


Overview of MK-2866


OTR-AC is the esterified version of the SARM MK-2866, otherwise known as Ostarine. Various animal-focused studies have shown that supplementation with Ostarine can have many positive benefits such as increased muscular vascularization and muscle metabolism. 


Ostarine and Muscle Growth

A notable study conducted by Roch et. Al, has studied the effect Ostarine has on 3-month-old female rats that were either kept intact or were ovariectomized. The rats were treated with Ostarine for 5 weeks and at the end of 5 weeks, the researchers measured changes in the weight in the uterus, gastrocnemius, and soleus muscles, as well as any changes to the size of the muscle fibers, the capillaries, and various enzyme activity.


Dosing with Ostarine had a positive effect on muscle vascularization and metabolism in the muscle. Additionally, Ostarine supplementation led to higher capillary density in the muscles and increased activity of citrate synthase in the gastrocnemius, and increased activity of lactate dehydrogenase in the longissimus muscle (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528560/). 


Process of Esterification

Esters are derived from carboxylic acids. The process of esterification entails replacing a hydroxyl group (-OH) with an alkyl (-O-) group. Esterification is considered a substitution reaction and is produced when the original carboxylic acid group is heated and in the presence of an acid catalyst. The most common acid used in these reactions is sulphuric acid, however, in special cases, acids such as hydrogen chloride can be used as the catalyst (https://www.chemguide.co.uk/organicprops/alcohols/esterification.html).  


Differences Between OTR-AC and MK-2866 

By adding an ester group to Ostarine, various benefits are added to the compound that is not seen in use with Ostarine alone. For example, when Ostarine undergoes an esterification reaction, the compound becomes more potent overall and the half-life is shown to have increased by more than 10 times the normal level, indicating that the ester version of Ostarine will be active for ten times as longer than the non-esterified version thus leading to additional benefits


Additionally, esters also act as emulsifiers. Generally, the job of emulsifiers is to reduce the surface tension between two liquids, and when the surface tension is reduced the mixture is considerably more stable. This phenomenon indicates that when Ostarine undergoes esterification it becomes a much more stable compound and could add additional benefits when being used for supplementation (https://www.acme-hardesty.com/esters-personal-care-market/).  


Our compounds are available in powdered, poly-cell, and standard polyethylene glycol formulations.  We employ an amphiphilic copolymer to form polymeric micelles that enhance the animal bioavailability of select SARMs. 


Furthermore, our nano-emulsification process ensures minimum polymeric micelle size and variance. Most importantly, our Poly-Cell Formula TM is optimized for sublingual absorption with a minimal taste profile. This stands in contrast to PEG, which is often intolerable for sublingual delivery due to its very unpleasant taste, leading to poor compliance among research participants. 


The primary concern for SARM researchers today is where to buy SARMS that are reliable and consistently pure. Umbrella Labs insures and guarantees its product purity by incorporating a process of Independent testing using Mass Spectrometry and Ultraviolet Radiation. Certificates of our product Independent tests are posted with our product descriptions.

Shipping Conditions: Ambient temperature.

Storage: Keep in a cool and dark location.



*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).





OTR-AC Certification of Authenticity COA

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Additional information

Weight 4 oz
Dimensions 3 × 3 × 5 in
Formula Option


Molar Mass

431.37 g·mol−1

Molecular Formula