Olga V. Konstantinova

Synthesis of [26-2H3]brassinosteroids

A number of [26-2H(3)]brassinosteroids were prepared for biochemical studies. The parent, nondeuterated compounds were considered to be biosynthetic intermediates in brassinosteroid biosynthesis. Claisen rearrangement was used to construct the steroidal side chain. Deuterium was introduced by reducing the corresponding intermediates with lithium aluminium deuteride.

Preparation of (25R)- and (25S)-26-functionalized steroids as tools for biosynthetic studies of cholic acids

A new synthesis of both epimeric forms of 26-cholestanoic acids and 26-alcohols containing a 3beta-hydroxy-Delta(5)- or a Delta(4)-3-keto-functionality in ring A is described starting from stigmasterol or (20S)-3beta-acetoxy-pregn-5-en-20-carboxylic acid. The obtained compounds are useful as standards for studies of cholic acids. Construction of the side chain was achieved by linkage of steroidal 23-iodides to sulfones prepared from (2R)- and (2S)-3-hydroxy-2-methylpropanoates. Oxidation of intermediate 26-alcohols into the corresponding carboxylic acids ensuring preservation of stereochemistry at C-25 and functional groups in the cyclic part was achieved with sodium chlorite catalyzed by TEMPO and bleach.

[3,3]-Claisen rearrangements in 24 alpha-methyl steroid synthesis - Application to campesterol, crinosterol, and delta(25)-crinosterol side chain construction

This paper elaborates an improved synthesis of crinosterol and campesterol starting from stigmasterol. The proposed approach is based on Claisen rearrangement of Delta23-22-allylic alcohols with various configurations of the 22-hydroxy group and geometry of the Delta23-double bond. It allows complete use of the starting steroid for preparing 24alpha-methyl derivatives. It was possible to partially control the stereochemistry at C-25. Hydrogenation of the Delta22-double bond was shown to proceed with partial isomerization of the C-24 alkyl substituent. The Ireland ester enolate variant of the Claisen rearrangement was demonstrated to be useful for preparing 24alpha-methyl steroids containing the Delta22,25-system.

Synthesis of hexadeuterated 23-dehydroxybrassinosteroids.

Two hexadeuterated brassinosteroids (BS) ([26,27-2H(6)]-23-dehydroxycastasterone and [26,27-2H(6)]-cathasterone) containing a hydroxy group at C(22) instead of the 22R,23R-diol function characteristic for most compounds of this class were prepared for biochemical studies. The corresponding non-deuterated compounds are considered intermediates in brassinolide biosynthesis. The carbon skeleton of the side chain with proper stereochemistry at C(24) was prepared from commercially available (2R)-3-hydroxy-2-methylpropanoate. This low molecular fragment was coupled to the tetracyclic steroidal fragment through the reaction of the appropriate sulfone with C(22) aldehyde. Formation of the necessary configuration of the 22-hydroxy group was achieved by hydride reduction of the corresponding ketone. Deuterium atoms at C(26) and C(27) originated from [2H(3)]methyl iodide used for alkylation of the intermediate sulfone.

Biosynthesis of 2,3-epoxybrassinosteroids in seedlings of Secale cereale

Two new brassinosteroids, (22R,23R,24S)-22,23-dihydroxy-24-methyl-5alpha-cholest-2-en-6-one (secasterol) and (22R,23R,24S)-22,23-dihydroxy-2alpha,3alpha-epoxy-24-methyl-5alpha-cholest-6-one (2,3-diepisecasterone) have been identified together with a known 2,3-epoxybrassinosteroid, secasterone, in seedlings of Secale cereale. Deuterated secasterol, teasterone, and typhasterol, upon administration to rye seedlings, were incorporated into secasterone and 2,3-diepisecasterone, indicating a biosynthetic route via teasterone/typhasterol to secasterol to 2,3-epoxybrassinosteroids.

Preparation and synthetic application of partially protected brassinosteroids

Preparation of partially protected brassinosteroids is achieved through the reaction of the source material (24-epicastasterone and 24-epibrassinolide) with diol-specific reagents (2,2-dimethoxypropane and methylboronic acid). The obtained products were shown to be useful synthetic intermediates for further preparation of minor representatives of this class of natural phytohormones (such as 3,24-diepicastasterone and 3-dehydro-24-epibrassinolide).

Synthesis of secasterol and 24-episecasterol and their toxicity for MCF-7 cells

The convergent synthesis of biosynthetic precursors of brassinosteroids with a Δ2-bond in cycle A—secasterol and 24-episecasterol—was performed. The key stages in the construction of the side chain in these compounds were the Julia olefination of the steroid 22-aldehyde followed by the Sharpless asymmetric dihydroxylation of the intermediate Δ22-olefin. The cytotoxicity of the synthesized compounds for breast carcinoma MCF-7 cells was assessed.

Synthesis of 24-Functionalized Oxysterols

The syntheses of (24S)-24,25-epoxycholesterol, (24S)-hydroxycholesterol, and 24-ketocholesterol are described. The compounds belong to oxysterols, which can be considered to be the modulators of cholesterol metabolism. The asymmetric hydroxylation of desmosterol acetate according to Sharpless was used as the key reaction in the stereoselective introduction of functionality in position 24.

Reversible conversion in the brassinosteroid quartet castasterone, brassinolide and their 3 beta-epimers

The metabolism of deuterated brassinosteroids has been studied in excised leaves of Secale cereale, and in vitro in seedlings of Arabidopsis thaliana and cell suspension cultures of Lycopersicon esculentum. In addition to the known biosynthetic conversion of castasterone to brassinolide and epimerization to 3-epicastasterone, inversion of the 3α-configured hydroxyl group of brassinolide to a 3β -configured one in 3-epibrassinolide has been observed using liquid chromatography (HPLC) with electrospray ionization (ESI) and selected ion-monitoring mass-spectrometry (SIM-MS). Administration of deuterated 3-epicastasterone and 3-epibrassinolide to Arabidopsis and Secale seedlings resulted in the formation of castasterone and brassinolide, respectively, indicating conversion of configuration at C-3 of brassinosteroids is reversible

Synthesis of C-5′-alkyl substituted 17-spirofuran 19-norsteroids

A number of new steroidal 17-spirofuran derivatives of the 19-nor series containing Me, Et or (i)Pr-substituents in the heterocyclic moiety has been prepared, which are expected to have a strong progestagenic activity. The proposed approach made use of the 1-3-dipolar cycloaddition of low-molecular nitrile oxides with steroidal acetylenic alcohols followed by transformation of the isoxazole side chain.