Abstract
This review concentrates on success stories from the synthesis of approved medicines and drug candidates using epoxide chemistry in the development of robust and efficient syntheses at large scale. The focus is on those parts of each synthesis related to the substrate-controlled/diastereoselective and catalytic asymmetric synthesis of epoxide intermediates and their subsequent ring-opening reactions with various nucleophiles. These are described in the form of case studies of high profile pharmaceuticals spanning a diverse range of indications and molecular scaffolds such as heterocycles, terpenes, steroids, peptidomimetics, alkaloids and main stream small molecules. Representative examples include, but are not limited to the antihypertensive diltiazem, the antidepressant reboxetine, the HIV protease inhibitors atazanavir and indinavir, efinaconazole and related triazole antifungals, tasimelteon for sleep disorders, the anticancer agent carfilzomib, the anticoagulant rivaroxaban the antibiotic linezolid and the antiviral oseltamivir. Emphasis is given on aspects of catalytic asymmetric epoxidation employing metals with chiral ligands particularly with the Sharpless and Jacobsen–Katsuki methods as well as organocatalysts such as the chiral ketones of Shi and Yang, Pages’s chiral iminium salts and typical chiral phase transfer agents.
Highlights
Epoxides are versatile electrophiles that support the stereospecific formation of ring-opened products with a wide array of nucleophiles
The implications of this reactivity in the context of drug design and desired biologic action as well as manifestation of adverse effects has been reviewed previously [1,2,3,4] these are best exemplified by the plethora of natural products and the 14 approved drugs containing the epoxide functionality [5,6]
What is lesser known is how pivotal has been the successful management of epoxide chemistry on scale leading to robust, cost-effective and safe manufacturing processes
Summary
Epoxides are versatile electrophiles that support the stereospecific formation of ring-opened products with a wide array of nucleophiles. From all interconnected routes discussed above (Scheme 9) and variations thereof, process chemists at Bristol-Myers Squibb selected to develop further the process from 27, that leads to the key epoxide 24 via intermediates 28, 32, 34 as the manufacturing route of choice for ravuconazole [49] This process that proceeds through the synthesis and ring opening of two epoxide intermediates has its roots in Sankyo’s original approach towards triazole antifungals and ever since has been regarded as the standard method to prepare these and related scaffolds [50,51,52,53,54]. IInn ccoonntrtaraststtottohitshriesqureirqeumireenmt,eancth, iraalcmhiarnagl amneasnegcaonmespelexco(Mm2p,leSxch(eMm2e,34S)cdheevmeelop3e4d) sdpeevceifilocpaelldy sfopretchifeiceaplloyxifdorattihoeneopfoexniodnaetisowniothf eHn2oOn2e,sswuffiithceHd2aOt20, .s2umffiocle%d taot e0p.2omxidoilz%e t(oS)e-pkeotxoindeiz1e2(1Si)n-k9e6t%onyei1e2ld, ibnut96at%dryi1e:7ldf,abvuortiantgdthr e1:u7nfdaevsoirreindgdtihaseteurnedoiessoimreedrdoifa1s1te9rae-osyisno(mSeart othfe1k1e9tao-nsyen, R(Satatthteheepkoextiodnee),[1R27a]t. the epoxide) [127]
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