Androstanes, conjugates

As first demonstrated by Stork,the metal enolate formed by metal-ammoni reduction of a conjugated enone or a ketol acetate can be alkylated in liquic ammonia. The reductive alkylation reaction is synthetically useful since ii permits alkylation of a ketone at the a-position other than the one at whicf thermodynamically controlled enolate salt formation occurs. Direct methyl-ation of 5a-androstan-17-ol-3-one occurs at C-2 whereas reductive methyl-... 

Enolizalion of conjugated or /3,y-unsatiirated enones and dienones in O-deiiterated solvents facilitates the introduction of deuterium labels into positions as far as three and five carbon atoms away from a given ketone function. Exchange of the activated hydrogens in androst-4-en-3-one (12) provides a good illustration of the potential of this method. Saturation of the double bond (section V) in the deuterated enone (13) followed by back exchange of the a-deuteriums (section II-B) proves to be an excellent method for the preparation of 6,6-d2-5a-androstan-3-one (15). ... 

The use of thiocyanic acid for thiirane synthesis is usually compatible with many functional groups found in natural steroids. The method has found application in androstanes, pregnanes, cholestanes, cholanates and cardeno-lides. However, the presence of a,j5-unsaturated carbonyl groups may decrease the yield of the thiocyanatohydrin due to conjugate addition of thiocyanic acid. Indeed, the 1,4-addition of thiocyanic acid has been carried... 

A series of conjugated polyenes capped with chromophores and containing an androstane spacer were synthesized by Wittig or Wittig-type olefinations from epi-androsterone 5150. For example, vinyl carboxaldehyde 52, prepared from 51 in 60% yield as shown in equation 32, was treated with 9-anthrylmethylphosphonium bromide and n-butyllithium to give diene 53. Exocyclic diene 53 was subsequently oxidized to vinyl carboxaldehyde 54. The androsterone vinyl aldehyde intermediate could either be treated with a tetraphenylporphyrinpolyenyl phosphonium ylide, or, as shown below, the phosphonium salt of the androsterone (55) could be reacted with TPP polyeneal 56. The desired all-(E) isomer, 57, was obtained from the ( )/(Z)-isomeric mixture by chromatographic purification. 

Major metabolite (glucuronic acid conjugate) 17a-Epimer 5a-Estrane-3) , 17a-diol 5a-Androstane-3) , 17a-diol 17a-Epimer... 

Disposition in the Body. Testosterone is the androgenic hormone formed in the testes. In man, it is metabolised to 5a-androstane-3a,17)5-diol, androsterone, etiocholanolone, and 5a-androstene-3,17-dione. In the horse, the major metabolites are 5a-androstane-3)5,17a-diol, which is excreted in the urine as the glucuronide conjugate, and the 17)5-epimer which is excreted in the urine as the sulphate conjugate. 

Reduction of ketones [1, 597-598, at end]. In a convenient preparation of 5a-androstane-16-one (4), Jones et al.lsa condensed 5a-androstane-17-one (1) with ben-zaldehyde to give the conjugated ketone (2). Then the 17-keto group was eliminated by reduction with Li AIH4-A1C13 and the product ozonized. Use of the hydride alone gave the 16-benzylidene-l 7/3-alcohol. This method has been applied also to the... 

The electrophilic Vilsmeier reagent (Me2N=CHOPOCl2), which readily formylates enolic ethers/ has now been found to react under more vigorous conditions with suitable dienes, or even with a 17-methylene-androstane (175) (Scheme 10), to give formyl derivatives e.g. 176). The over-all reaction is one of substitution, via electrophilic addition followed by deprotonation, which is favoured by conjugation in the final product (Scheme 10). A most significant... 

The establishment of NRs pregnane X receptor (PXR) and constitutive androstane receptor (CAR) as xenobiotic receptors was published in 1998 [1,2], PXR and CAR were initially found to regulate the phase ICYP3 A and CYP2B enzymes. Subsequent studies have shown that both receptors can also regulate the expression of phase II conjugating enzymes and phase III drug transporters and for this reason, PXR and CAR have been proposed to function as master xenobiotic receptors. 

The stereoselectivity of the hydride reduction of conjugated cyclohexenones has also been subjected to close examination from both experimental and theoretical viewpoints. Much of the work has involved polycyclic systems, e.g.. steroids which have little conformational flexibility and in which axial and equatorial directions of approach can be clearly defined. With small" hydride donors, these substrates show an even clearer preference for axial attack than the corresponding cyclohexanones. For examples involving reductions with lithium aluminum hydride and sodium borohydride, see Table 10. 3/(-Acetylcholest-5-en-7-one and cholest-2-en-l-one are notable in that the analogous saturated substrates are attacked from the equatorial direction115 l16. The reduction of 17/i-hydroxy-4-androsten-3-one (testosterone) to 4-androstene-3/1,17/j-diol with d.r. 90 10 can be compared with the sodium borohydride reduction of 17/i-hy-droxyandrostan-3-one (dihydrotestosterone) to androstane-3/ ,17/ -diol with d.r. 81 19 (see p 4030). 

Using countercurrent distribution Hadd and Dorfman (1963) have isolated 5a-androstan- and crystalline 5/8-androstan-[(3a —> l/S-oside)-D-glucopyranosuronic acids]-17-one from the urine of a woman with an adrenal adenoma. They characterized these conjugates and their triacetyl methyl esters by infrared absorption, optical rotation, and melting point methods. 

Sites of Reaction. Reduction of conjugated double bonds was first observed by Mamoli and Schramm (M-548) with a crude culture of putrefactive bacteria. The pure culture, described as Bacillus putrificus, reduced 3-keto-A -androstenes to 3-keto-5 -androstanes and Sa-hydroxy-S S-androstanes (M-545). This culture is no longer available (E-202), but a modern equivalent is Clostridium paraputrificum, described by Schubert (Ap-71, S-823). The properties of the latter are described in greater detail in the section on reduction of carbonyl groups. 

Most conjugation reactions take place in the liver after being metabolized by reductive enzymes, the steroids are conjugated by sulfo- or glucu-ronyltransferases. The hydrogenated metabolites of corticosteroids and many 3a,5a-reduction products of the pregnane and androstane series. 

FIG. 5 A sterol-polyoxyethylene conjugate synthesized by Stadler and coworkers [45], This compound, 5-androstane-3p,17p-bis((oxycarbonyl)hexaethylene glycol), was designed as a prototype for a new class of compounds intended to serve as functional equivalents to the antiobiotic drug amphotericin B. 

We are able to determine two steroid conjugates, 5a-androstane-3a,17p diol glucuronide (ADG) and DHEA-S by ID-GC-MS. Cleavage of the conjugate group is required prior to GC [2], The released free steroids are analyzed according to the GC-MS conditions described above. 

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