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OTR-AC (aka MK-2866 Ester)



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


When the SARM MK-2866 (Ostarine) undergoes the process of esterification, it becomes OTR-AC. Studies involving both male and female rats have found that when dosed with MK-2866, there are many different reported benefits such as an increase in muscle metabolism and vascularization. 


In a noteworthy research experiment conducted by Roch et. Al, 3-month-old female rats, either intact or ovariectomized, were given MK-2866 over the course of 5 weeks. After the 5 weeks were up, the researchers measured any notable changes in muscle fiber size, enzyme activity, and capillary density, as well as any weight changes in the uterus, gastrocnemius, and soleus muscles.


The results of the study found that when supplemented with MK-2866, female rats had an increase in muscle vascularization and muscle metabolism. Furthermore, use of MK-2866 resulted in increased citrate synthase activity in the gastrocnemius, increased lactate dehydrogenase activity in the longissimus muscle, and an overall increase in capillary density in the muscles that were being measured (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528560/). 


Process of Esterification

The process of esterification is considered a substitution reaction where the end-product esters are derived from carboxylic acids and the hydroxyl group (-OH) of the compound is replaced with an alkyl (-O-) group. This process occurs when the carboxylic acid in the original compound is exposed to heat and an acid catalyst. In the process of esterification, the most common acid catalyst used is sulphuric acid, however, there are certain cases where hydrogen chloride can be used instead (https://www.chemguide.co.uk/organicprops/alcohols/esterification.html).  


Differences Between OTR-AC and MK-2866

After creating the ester version of MK-2866, there are many added benefits to the resulting compound that are not reported when undergoing treatment with MK-2866 alone. For example, the esterification of MK-2866 leads to the compound not only being considered more potent but also leads to at least a 10-fold increase in the half-life of the compound. When the half-life is increased by more than 10 times the normal rate, the compound is active for more than ten times as long as MK-2866. 


An additional benefit to esters is their ability to act as emulsifiers. The goal of using an emulsifier is to reduce surface tension between two liquids, such as oil and water. When the surface tension is reduced due to an emulsifying agent, the mixture is far more stable. By supplementing with the esterified version of MK-2866, OTR-AC, the compound is more stable, thus indicating the presence of a multitude of additional benefits not found in MK-2866 by itself (https://www.acme-hardesty.com/esters-personal-care-market/).  


OTR-AC Availability

We find many researchers prefer flexibility in their compounds and we are proud to offer three different formulations that will meet your research needs: powdered, poly-cell, and standard polyethylene glycol (PEG).  Our powdered formulation is ideal for researchers who wish to have the flexibility to reconstitute the compound in the diluent that best suits their research goals. 


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).



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[2] T. N. Ziegenfuss, J. M. Berardi, L. M. Lowery, and J. Antonio, “Effects of prohormone supplementation in humans: A review,” Can. J. Appl. Physiol., 2002.

[3] F. F. Ip, I. Di Pierro, R. Brown, I. Cunningham, D. J. Handelsman, and P. Y. Liu, “Trough serum testosterone predicts the development of polycythemia in hypogonadal men treated for up to 21 years with subcutaneous testosterone pellets,” Eur. J. Endocrinol., 2010.

[4] A. A. Yassin and M. Haffejee, “Testosterone depot injection in male hypogonadism: a critical appraisal.,” Clinical interventions in aging. 2007.

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[6] K. L. Johansen, P. L. Painter, G. K. Sakkas, P. Gordon, J. Doyle, and T. Shubert, “Effects of resistance exercise training and nandrolone decanoate on body composition and muscle function among patients who receive hemodialysis: A randomized, controlled trial,” J. Am. Soc. Nephrol., 2006.

[7] J. H. MacDonald, S. M. Marcora, M. M. Jibani, M. J. Kumwenda, W. Ahmed, and A. B. Lemmey, “Nandrolone decanoate as anabolic therapy in chronic kidney disease: A randomized phase II dose-finding study,” Nephron – Clin. Pract., 2007.

[8] C. Hassager, J. Pødenphant, B. J. Riis, J. S. Johansen, J. Jytte, and C. Christiansen, “Changes in soft tissue body composition and plasma lipid metabolism during nandrolone decanoate therapy in postmenopausal osteoporotic women,” Metabolism, 1989.

[9] “Anabolics – William Llewellyn – Google Books.” [Online]. Available: https://books.google.com/books?id=afKLA-6wW0oC&pg=PT402#v=onepage&q&f=false. [Accessed: 17-Jul-2020].

[10] R. S. Gudde and J. R. Addicam, “Comparative evaluation of testosterone release and its derivatives in adult male monkeys,” Open Androl. J., 2012.

[11] T. Piper et al., “Studies on the in vivo metabolism of the SARM YK11: Identification and characterization of metabolites potentially useful for doping controls,” Drug Test. Anal., 2018.

Buy SARMs for sale like our OTR-AC (MK-2866 ESTER) SARM POWDER – 1000MG / 1 GRAM from UMBRELLA Labs and enjoy the highest quality and purity OTR-AC SARMs available online.



Pure ACP-105 SARM Powder For Sale Side 1 Pure OTR-AC SARM Powder 1000MG For Sale Pure OTR-AC SARM Powder 1000MG For Sale










OTR-AC Certification of Authenticity COA


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Additional information

Weight 2 oz
Dimensions 3 × 3 × 5 in