A new route to 19-substituted steroids from 19-nor steroids: Sigmatropic [3,3] and [2,3] rearrangements revisited

Modular ketal-linked prodrugs and biomaterials enabled by organocatalytic transisopropenylation of alcohols

Isopropenyl ethers are critical intermediates for accessing medicinally valuable ketal-based prodrugs and biomaterials, but traditional approaches for the synthesis of isopropenyl ethers suffer from poor functional group compatibility and harsh reaction conditions. Here, we develop an organocatalytic transisopropenylation approach to solve these challenges, enabling the synthesis of isopropenyl ethers from various hydroxyl-group-containing small-molecule drugs, polymers, and functional building blocks. The method provides a straightforward and versatile synthesis of isopropenyl ethers, features excellent tolerance of diverse functional groups, applies to a wide range of substrates, and allows scalable synthesis. The development of this organocatalytic transisopropenylation approach enables access to modular preparation of various acid-sensitive ketal-linked prodrugs and functionalized ketalated biomaterials. We expect our syntheses and transformations of isopropenyl ethers will find utility in several diverse fields, including medicinal chemistry, drug delivery, and biomaterials.

Isopropenyl ethers (IPPEs) are essential intermediates for obtaining ketal-based prodrugs and biomaterials, but traditional approaches for their synthesis are limited by poor functional group compatibility and harsh reaction conditions. Here, the authors report an organocatalytic transisopropenylation approach for IPPE synthesis in mild reaction conditions and with wide range of substrates, and use it to prepare acid-sensitive ketal-linked prodrugs and biomaterials.

6,19-carbon-bridged steroids. Synthesis of 6,19-methanoprogesterone

6,19-Methanoprogesterone (4) was synthesized in nine steps from the readily available 3 beta,20 beta-diacetyloxy-5 alpha-bromo-6,19-oxidopregnane (5) in 14% overall yield. The additional carbon atom was introduced by reaction of a C-19 aldehyde with Ph3PCHOCH3 under salt free conditions and subsequent hydrolysis to give the homologous aldehyde. Intramolecular addition of the newly incorporated carbonyl (C-19a) to the olefinic C-6 in ring B was achieved by means of a Prins reaction with TiCl4 as Lewis acid.

Structure-activity relationships of a new family of steroidal aromatase inhibitors. 1. Synthesis and evaluation of a series of analogs related to 19-[(methylthio)methyl]androstenedione (RU54115)

During the course of a study aimed at the search for new potent aromatase inhibitors, several new androstenedione analogs were synthesized and evaluated. This study led to the discovery of 19-[(methylthio)methyl]androsta-4,9(11)-diene-3,17-dione (7; RU54115) already described by our laboratory. The object of the present series of papers is to disclose the result of the structure-activity relationship studies that gave rise to this compound. This first part deals mainly with the substitution in the 19-position of the steroid nucleus. Several parameters were varied, the length of the chain and its rigidity and branching, as well as the nature of the heteroatom itself and its substitution. The interaction of these new compounds with human placental aromatase in competition with the substrate androstenedione was studied by difference visible spectroscopy. The in vivo aromatase-inhibiting activities were evaluated by measuring the estradiol lowering after oral administration of the compounds to PMSG-primed female rats.