Selective Hydroxylation of C(sp³)−H Bonds in Steroids

Abstract

Steroids are highly prevalent structures in small‐molecule therapeutics, with the level of oxidation being key to their biological activity and physicochemical properties. These C(sp3)‐rich tetracycles contain many stereocentres, which are important for creating specific vectors and protein binding orientations. Therefore, the ability to hydroxylate steroids with a high degree of regio‐, chemo‐ and stereoselectivity is essential for researchers working in this field. This review will cover three main methods for the hydroxylation of steroidal C(sp3)−H bonds: biocatalysis, metal‐catalysed C−H hydroxylation and organic oxidants, such as dioxiranes and oxaziridines.

Recent developments in the enzymatic modifications of steroid scaffolds

“…Hydroxylation of steroids stands as one of the most pivotal reactions in modifications of the steroid scaffold. [15][16][17] The addition of hydroxy groups not only influences physiological functions, polarity, solubility, and toxicity but also serves as a synthetic starting point for the preparation of valuable steroid drugs. 18,19 In this section, we discuss recent advances in the discovery and engineering of cytochrome P450 oxygenases (P450s), non-heme iron-and α-ketoglutarate-dependent oxygenases (αKG OXs), Rieske oxygenases, and other enzymes for site-specific hydroxylations.…”

“…18,19 In this section, we discuss recent advances in the discovery and engineering of cytochrome P450 oxygenases (P450s), non-heme iron-and α-ketoglutarate-dependent oxygenases (αKG OXs), Rieske oxygenases, and other enzymes for site-specific hydroxylations. For a comparative summary elucidating the preference sites for enzymatic hydroxylation of steroids, readers are directed to the 2020 review by Zhang et al, the 2022 review by Zhu et al and the 2023 review by Abas et al [15][16][17] 2.1 P450s C-14 functionalized steroids, encompassing 14α-OH and 14β-OH substituted steroids, are widely distributed in nature and exhibit significant biological activities, as evidenced by drugs such as the cardiac glycosides digoxin (1), digitoxigenin (2), and bufotalin (3), and the veterinary drug proligestone (4) (Fig. 1A).…”

“…18,19 In this section, we discuss recent advances in the discovery and engineering of cytochrome P450 oxygenases (P450s), non-heme iron- and α-ketoglutarate-dependent oxygenases (αKG OXs), Rieske oxygenases, and other enzymes for site-specific hydroxylations. For a comparative summary elucidating the preference sites for enzymatic hydroxylation of steroids, readers are directed to the 2020 review by Zhang et al , the 2022 review by Zhu et al and the 2023 review by Abas et al 15–17…”

Biocatalytic Steroidal 9α‐Hydroxylation and Fragmentation Enable the Concise Chemoenzymatic Synthesis of 9,10‐Secosteroids

“…[5] We envisioned that a short entry into 1 could be achieved through a biomimetic, strategic C9À C10 bond disconnection by dienone-phenol fragmentation (Figure 1), and 9α-hydroxylated dienone 4 was revealed as the key intermediate. While various steroidal hydroxylation strategies have been developed, [6] 9α-hydroxylation remains an unmet challenge due to the inherent inertness of the C9-H bond and the associated steric hindrance. Classical chemical methods normally suffer from low synthetic efficiency due to extensive prefunctionalization, harsh reaction conditions, and the need for multiple steps.…”

“…[7] In contrast, biocatalytic CÀ H oxidation has emerged as a promising alternative to address these challenges. [6,8] Accordingly, chemoenzymatic strategy has emerged as an attractive strategy in the synthesis of biologically active natural products and their analogs, [9] including several steroids (Figure S5). [8] To date, only a very few biocatalysts have been demonstrated to catalyze steroidal C9-H hydroxylation, including several certain microorganisms, such as Pseudomonas sp.…”