Stereoselective syntheses of 20-epi cholanic acid derivatives from 16-dehydropregnenolone acetate

The Corey-Seebach Reagent in the 21st Century: A Review

The Corey-Seebach reagent plays an important role in organic synthesis because of its broad synthetic applications. The Corey-Seebach reagent is formed by the reaction of an aldehyde or a ketone with 1,3-propane-dithiol under acidic conditions, followed by deprotonation with n-butyllithium. A large variety of natural products (alkaloids, terpenoids, and polyketides) can be accessed successfully by utilizing this reagent. This review article focuses on the recent contributions (post-2006) of the Corey-Seebach reagent towards the total synthesis of natural products such as alkaloids (lycoplanine A, diterpenoid alkaloids, etc.), terpenoids (bisnorditerpene, totarol, etc.), polyketide (ambruticin J, biakamides, etc.), and heterocycles such as rodocaine and substituted pyridines, as well and their applications towards important organic synthesis.

Synthesis of novel pregnane-based 20-carboxamides via palladium-catalysed aminocarbonylation

20-Carboxamidopregnene derivatives, such as 3β-acetoxy-5α-pregn-20-ene-20-carboxamides and 5α-pregn-20-ene-20-carboxamides were synthesized from the widely accessible 3β-acetoxy-pregn-5,16-dien-20-one (PDA) using selective hydrogenation, hydrazine and iodoalkene formation, as well as palladium-catalysed aminocarbonylation. The 20-iodo-20-ene derivatives, obtained from the corresponding 20-keto derivatives via their hydrazones, served as substrates. 23 new 20-carboxamides were obtained using various N-nucleophiles ranging from simple primary amines to α-amino acid esters. The novelty of this methodology lies in the application of facile, moderate or high-yielding reactions to obtain otherwise hardly accessible steroidal 20-carboxamides of pharmaceutical importance. In other words, instead of the enzymatic or synthetic degradation of e.g., sterols or cholanic acids, functionalization of the basic skeleton (a ‘building-up’ approach) was used.

A streamlined synthesis of the neurosteroid 3β-methoxypregnenolone assisted by a statistical experimental design and automation

The potential of integrating flow synthesizers, statistical design of experiments and automation has been exemplified to realize the streamlined etherification of pregnenolone to the neurosteroid 3β-methoxypregnenolone (MAP4343).

Melanogenesis Inhibitors from the Rhizoma of Ligusticum Sinense in B16-F10 Melanoma Cells In Vitro and Zebrafish In Vivo

The rhizoma of Ligusticum sinense, a Chinese medicinal plant, has long been used as a cosmetic for the whitening and hydrating of the skin in ancient China. In order to investigate the antimelanogenic components of the rhizoma of L. sinense, we performed an antimelanogenesis assay-guided purification using semi-preparative HPLC accompanied with spectroscopic analysis to determine the active components. Based on the bioassay-guided method, 24 compounds were isolated and identified from the ethyl acetate layer of methanolic extracts of L. sinense, and among these, 5-[3-(4-hydroxy-3-methoxyphenyl)allyl]ferulic acid (1) and cis-4-pentylcyclohex-3-ene-1,2-diol (2) were new compounds. All the pure isolates were subjected to antimelanogenesis assay using murine melanoma B16-F10 cells. Compound 1 and (3S,3aR)-neocnidilide (8) exhibited antimelanogenesis activities with IC₅₀ values of 78.9 and 31.1 μM, respectively, without obvious cytotoxicity. Further investigation showed that compound 8 demonstrated significant anti-pigmentation activity on zebrafish embryos (10‒20 μM) compared to arbutin (20 μM), and without any cytotoxicity against normal human epidermal keratinocytes. These findings suggest that (3S,3aR)-neocnidilide (8) is a potent antimelanogenic and non-cytotoxic natural compound and may be developed potentially as a skin-whitening agent for cosmetic uses.

Allimacrosides A-E, new steroidal glycosides from Allium macrostemon Bunge

A new pregnane-type steroidal glycoside (1), two new spirostane-type steroidal glycosides (2, 3), and two new furostane-type steroidal glycosides (4, 5), named allimacrosides A-E, together with four known compounds (6-9) were isolated from a 80% MeOH extract of Allium macrostemon Bunge. The identification and structural elucidation of these compounds were based on their 1D- and 2D-NMR spectra, and HR-FAB-MS data analysis. The isolated compounds were tested for cytotoxicity against four human tumor cell lines in vitro using the sulforhodamine B bioassay.

Isotope-Labeling Studies Support the Electrophilic Compound I Iron Active Species, FeO(3+), for the Carbon-Carbon Bond Cleavage Reaction of the Cholesterol Side-Chain Cleavage Enzyme, Cytochrome P450 11A1

The enzyme cytochrome P450 11A1 cleaves the C20-C22 carbon-carbon bond of cholesterol to form pregnenolone, the first 21-carbon precursor of all steroid hormones. Various reaction mechanisms are possible for the carbon-carbon bond cleavage step of P450 11A1, and most current proposals involve the oxoferryl active species, Compound I (FeO(3+)). Compound I can either (i) abstract an O-H hydrogen atom or (ii) be attacked by a nucleophilic hydroxy group of its substrate, 20R,22R-dihydroxycholesterol. The mechanism of this carbon-carbon bond cleavage step was tested using (18)O-labeled molecular oxygen and purified P450 11A1. P450 11A1 was incubated with 20R,22R-dihydroxycholesterol in the presence of molecular oxygen ((18)O2), and coupled assays were used to trap the labile (18)O atoms in the enzymatic products (i.e., isocaproaldehyde and pregnenolone). The resulting products were derivatized and the (18)O content was analyzed by high-resolution mass spectrometry. P450 11A1 showed no incorporation of an (18)O atom into either of its carbon-carbon bond cleavage products, pregnenolone and isocaproaldehyde . The positive control experiments established retention of the carbonyl oxygens in the enzymatic products during the trapping and derivatization processes. These results reveal a mechanism involving an electrophilic Compound I species that reacts with nucleophilic hydroxy groups in the 20R,22R-dihydroxycholesterol intermediate of the P450 11A1 reaction to produce the key steroid pregnenolone.

Total synthesis of starfish saponin goniopectenoside B

Star quality: Goniopectenoside B, a minor asterosaponin from starfish Goniopecten demonstrans with antifouling activity, has been synthesized in a convergent 21 steps and in 4.3 % overall yield starting from adrenosterone. This represents the first synthesis of a complex asterosaponin, which are ubiquitous and characteristic in starfish as defense chemicals (see figure).

Access to functionalized steroid side chains via modified Julia olefination

Various functionalized steroidal side chains were conveniently accessed by a modified Julia olefination strategy using a common sulfone donor and an appropriate α-branched aldehyde acceptor. For the coupling of these hindered classes of reaction partners (and in contrast to typically observed trends), the benzothiazolyl(BT)-sulfone anion gave superior outcomes compared to the phenyltetrazolyl(PT)-sulfone anion.

Microbial transformation of 3β-acetoxypregna-5,16-diene-20-one by Penicillium citrinum

The biotransformation of 3β-acetoxypregna-5,16-diene-20-one (1) by using a filamentous fungus Penicillium citrinum resulted in the production of four metabolites 2-5. The structures of these compounds were elucidated by different spectroscopic analysis (1D- and 2D-NMR) and HR-ESI-MS as 3β,7β-dihydroxy-pregn-5,16(17)-dien-20-one (2), 3β-hydroxy-7α-methoxy-pregn-5,16(17)-dien-20-one (3), 3β,7β,11α-trihydroxy-pregn-5,16(17)-dien-20-one (4), and a known 3β,7α-dihydroxy-pregn-5,16(17)-dien-20-one (5). The 7-O-methylation is a novel reaction in the field of microbial transformation of pregnane steroids.