Caronic anhydride, also known as 6,6-Dimethyl-3-oxabicyclo[3.1.0]hexane-2,4-dione, is a pharmaceutical intermediate mainly used as a synthesis of Boceprevir, an oral protease inhibitor of hepatitis C. The molecular structure of Boceprevir includes three fragments: P1, P2 and P3 (Figure 1). Caronic anhydride is the raw material for the synthesis of fragment P2.

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Figure 1. Structure of Boceprevir

Pfizer's COVID-19 oral drug, Paxlovid, also has a molecular structure that includes fragment P2 (Figure 2). So, caronic anhydride (CAS NO.67911-21-1) is also the starting material for Paxlovid. Paxlovid is a new oral antiviral medication to treat mild-to-moderate COVID-19 disease in people who are at high risk for severe COVID-19. Huateng Pharma provides 99+% high purity caronic anhydride with a production capacity of 20 tons per month. We can also provide CDMO services for COVID-19 drugs with sufficient capacity. Contact us at sales@huatengusa.com now. 

​Figure 2. Paxlovid Structure

Paxlovid (PF-07321332) is a combination of two drugs that must be taken together: Nirmatrelvir, which blocks an enzyme needed for the SARS-CoV-2 virus to reproduce, and ritonavir, a commonly used HIV treatment. In the Paxlovid combination, ritonavir slows the breakdown of nirmatrelvir so it works longer. The three pills must be taken twice a day for five consecutive days.​

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References:
1. Li, T.; Liang, J.; Ambrogelly, A.; Brennan, T.; Gloor, G.; Huisman, G.; Lalonde, J.; Lekhal, A.; Mijts, B.; Muley, S.Efficient, Chemoenzymatic Process for Manufacture of the Boceprevir Bicyclic [3.1.0]Proline Intermediate Based on Amine Oxidase-Catalyzed Desymmetrization. J. Am. Chem. Soc. 2012, 134, 6467,  DOI: 10.1021/ja3010495
​2. Pfizer’s Novel COVID-19 Oral Antiviral Treatment Candidate Reduced Risk of Hospitalization or Death by 89% in Interim Analysis of Phase 2/3 EPIC-HR Study, https://www.pfizer.com/news/press-release/press-release-detail/pfizers-novel-covid-19-oral-antiviral-treatment-candidate