Androstanes

Both reversed phase and normal phase chromatography have been used for the separation of the androstanes. In general normal phase chromatography using unmodified silica as the stationary phase is the preferred mode of separation since better resolution of all the epimeric steroids except the 17-epimers can be achieved (Hunter et al., 

An example of the use of normal phase chromatography to resolve a mixture of androgens is shown in Fig. 11.6.3. Resolution of the epimers of the monohydroxy metabolites of testosterone and androstanedione has been achieved using a mobile phase of hexane-tetrahydrofuran-2-propanol (80 15 5) with a silica stationary phase (Kawalek et al., 1981). 

The ability of reversed phase HPLC to resolve the androstanes is 

The most convenient method of detection of the androstanes is to utilise their characteristic UV absorbance. The d -3-ketones (including androstenedione and testosterone) have a strong absorption at 254 nm such that as little as 30 ng of testosterone can be detected. The 

17-ketosteroids (including androsterone and etiocholanolone) can be monitored at 280 nm but the sensitivity of detection is five-times less than that of the 4 -3-ketones (Hunter et al., 1979). 

Steroids that possess angular methyl groups at both the 10 and 13 positions but which are devoid of acetyl side chains at the 17 position are usually classed as derivatives of the hypothetical hydrocarbon, androstane. The endogenous male sex hormones, such as, for example, testosterone, can all be classified as androstanes as will be noted below, the biological activity of compounds in this stmctural class goes beyond that narrow definition. 

The androstane nucleus is sufficiently complex so as to effectively mle out total synthesis as a commercial source for starting materials. The great preponderance of steroid natural products includes carbon side chains at the 17 position. Preparation of androstane starting compounds thus relies on schemes for degrading those side 

More recent work in the corticosteroid senes has involved modification of the dihydrox-yacetone side chain at the 17 position Activity is retained, for example, when the hydroxyl group at the 17 position is omitted Thus, addition of the elements of hypobromous acid to tnene 36 [8], gives the bromohydnn 37, treatment with base leads to internal elimination to form the p-epoxide 38, opening of the oxir.ine with hydrogen fluoride gives desoximetasone, 39, [9] 

Condensation of prednisone, 40 with tetraethyl orthocarbonate leads to the cyelie ortho-carbonate 41 liydrolysis proceeds by protonation on the most accessible ether oxygen (that on carbon 21) to give the 17 mixed carbonate ester 42. Acylation with propionyl chloride proceeds on the remaining hydroxyl group to afford prednicarbate (43) [10], 

Activity is also retained when the hydroxyl group at the 21 position is replaced by chlorine. Reaction of corticoid 44 with methanesulfonyl chloride proceeds preferentially at the 21-hydroxyl (45) due to the hindered nature of the 11-alcohol. Replacement of the mesylate by means of lithium chloride in DMF affords clobetasol propionate (46) a similar sequence starting with the 17- butyrate ester 47, via mesylate 48, should give clobetasone butyrate, (49) [11]. 

In a similar vein, acylation of the corticoid 50 with furoyl chloride gives the diacyl derivative 51. Reduction with sodium borohydride serves to convert the 11-ketone to the alcohol 52. Hydrolysis under mild acid conditions preferentially removes the acyl group at the less hindered 21 position. The hydroxyl group in that derivative (53) is then converted to the mesylate 54. Replacement by chlorine affords mometasone (55) [12]. 

Activity is also retained when oxygen at the 21 position is replaced by sulfur. Preparation of one of these compounds follows a route quite analogous to the foregoing thus, displacement of the mesylate group in the cortisone (56) derivative 57 with the anion from thiopivalic acid affords thioester 58. Reduction of the 11-ketone by means of borohydride affords tixocortol pivalate (59)[13j. 

Halogenation of steroid 3-ketones can lead to complicated mixtures by virtue of the fact that the kinetic enol leads to 3 halo products, whereas the thermodynamic product is that halogenated at the 4 position. Carefully controlled reaction of the 5a-androstanolone with chlorine thus leads to the 2a-chloro derivative (29). Reaction of that intermediate with O(p-nitrophenyl)-hydroxylamine affords the androgenic agent ni stremine acetate (30).  

A highly modified methyl testosterone derivative also exhibits antiandrogenic activity. One synthesis of this compound Involves initial alkylation of methyl testosterone (3 ) by means of strong base and methyl iodide to afford the 4,4-dimethyl derivative Formylation with alkoxide and 

The synthesis of 4,4-dimethyl-5a-androstan-17j8-ol-3-one and its 19-nor-analogue employed methylation of the 2,2-trimethylenedithian derivatives and subsequent desulphurization. It was confirmed that catalytic hydrogenation of 

Toscano, G. Grisanti, G. Fioriello, L. Barlotti, A. Bianchetti, and M. Riva, J. Medicin. Chem., 1977, 20,213. 

In Apocynaceae pregnenolone is the precursor of alkaloids of the holarrhimine and conarrhimine types. 

Holarrhimine and related alkaloids may be used in the preparation of corticosteroids used in medicine. 

Alkaloids of neotropical poison frogs. Prog. Chem. Org. Nat. Prod. 4i, 205-340 (1982) 

Grunwald, C. Sjteroids. In Encyclopedia of Plant Physiology, New Series, Vol. 8, Secondary Plant Products (E. A. Bell, B. V. Charlwood, eds.), pp. 221-256. Springer, Berlin-Heidelberg-New York 1980 

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Ketopregnan-21-oic Acids, the 17(3-Carboxy Androstanes, and the D-Homocorticoids. In the course of studies on the metabohsm of fluocoitolone (103) the formation of the water-soluble carboxyhc acid (105, R = H) was reported. As a free 21-hydroxyl is not necessary for antiinflammatory activity, it was concluded that the esters (105, R = alkyl) of the preceding metabohte would possess antiinflammatory activity on topical administration but would be devoid of systemic activity when hydrolysis to the free acid occurs followed by... 

Methods for reconstmcting the C-17 side chain from intermediates such as androstendione have been developed. These are used when commercial considerations favor the production of androstanes, but pregnanes are the ultimate goal (25,30). 

A number of steroids have been regioselectively acylated ia a similar manner (99,104). Chromobactenum viscosum hpase esterifies 5a-androstane-3P,17P-diol [571-20-0] (75) with 2,2,2-triduoroethyl butyrate ia acetone with high selectivity. The hpase acylates exclusively the hydroxy group ia the 3-position giving the 3P-(monobutyryl ester) of (75) ia 83% yield. In contrast, bacillus subtilis protease (subtihsia) displays a marked preference for the C-17 hydroxyl. Candida iylindracea]i 2Lse (CCL) suspended ia anhydrous benzene regioselectively acylates the 3a-hydroxyl group of several bile acid derivatives (104). 

The reaction of 6-amino-5-(l,2-diethoxycarbonylhydrazino)pyrimidines with enamines represents another convenient method for the preparation of pteridines. Fusion of 5-(l,2-diethoxycarbonylhydrazino)-2,4,6-triaminopyrimidine (281) with an excess of mor-pholinocyclohexene leads to 2,4-diaminotetrahydrobenzo[g]pteridine, and with the morpholinoenamine (282) from 17/3-hydroxy-5a-androstan-3-one regioselective condensation to the fused pteridine (283) takes place in almost quantitative yield (equation 101) (71CC83). 6-Amino-5-nitroso- and 6-amino-5-phenylazo-pyrimidines react similarly, imitating the Timmis-type reaction (72CPB1428). 

In 1959 Clinton and coworkers reported the first synthesis of some pyrazole fused androstane derivatives and described their biological activity (B-76MI40404). Stanazolol (695) or 17-methyl-2iT-5o -androst-2-eno[3,2-c]pyrazol-17/3-ol was 10 times as active as 17a -methyltestosterone in improving nitrogen retention in rats (B-80MI40406), and its myotrophic activity was only twice that of 17a-methyltestosterone. It is used as an anabolic steroid with no lasting adverse side effects. 

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-... 

The presence of an a-bromo substituent may cause anomalies. With NaBH4, 2a-bromo-5a-cholestan-3-one gives a mixture of epimers, in which the 3p-o predominates. 4 -Bromo-17)5-hydroxy-5)5-androstan-3-one acetate gives 25% of the 315,4 -bromohydrin and 34% of the 3a,4)5-compound. Reduction of 7a-bromo-3)5,5a-diacetoxycholestan-6-one gives exclusively 7a-bromocholestane-3)5,5a,6a-triol 3,5-diacetate,whereas reduc-... 

There is no generally reliable rule of thumb to predict whether an axial or equatorial proton will exchange faster. For instance, in the examples discussed above, the slowest rate of exchange is found for the S -axial proton in 5a-androstan-7-one (1) [see(2)-(4)] and the 2fi-equatorial proton in 5a-androstan-l 1-one (5) [see (6)-(9)]. Furthermore, the results of base-catalyzed exchange cannot necessarily be predicted from the corresponding... 

Deuteration of 3 -Hydroxy-5a-androstan-7-one at C-6 and C-8 by Exchange with Deuterium Oxide-5% Sodium Deuterioxide in Methanol-OD... 

A solution of 3j5-hydroxy-5a-androstan-7-one (10, 50 mg) in methanol-OD (4 ml) is saturated with deuterium oxide containing 5 % sodium deuterioxide (prepared by reacting sodium with deuterium oxide) and heated under reflux for 3 days. (If the heated solution becomes turbid due to supersaturation, a few drops of methanol-OD should be added until a clear solution is obtained. The use of a drying-tube on top of the condenser is advisable to avoid isotope dilution from moisture.)... 

After cooling, the reaction mixture is diluted with ether, the organic phase washed with ice-cold water and dried over anhydrous sodium sulfate. Evaporation of the solvent and crystallization of the residue from ether-hexane gives 6,6,8j5-d3-5a-androstan-3j5-ol-7-one (11) in 84% yield mp 141-142,5° isotopic composition 6% d2,93% da and 1 %... 

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). ... 

It has been reported recently that 17/ -acetoxy-5a,14a-androstan epimerizes at C-14 when photolyzed in cyclohexane solution in the presence of mercuric bromide. When the reaction is carried out in perdeuterated cyclohexane, the product consists of 55 % d - and 12% d2-labeled species. This reaction may develop into an interesting deuteration technique if the incorporated deuterium can be securely assigned to the epimerized position. 

The successful preparation of Il,ll-d2-5l5-androstan-3o -oh and 11,11-d2-(25R)-5a-spirostane in 83% and 91% isotopic purity by Raney nickel treatment of the 11,1 l-d2-12-ethylene thioketal derivatives further confirms the low degree of isotope scrambling with C-12 keto steroids. 

Deuteration at C-3 by Reduction of 5a.-Androstan-3-one Oxime with Lithium Aluminum Deuteride... 

A solution of 5a-androstan-3-one oxime (112 0.6 g) in dry ether (40 ml) is added dropwise to a boiling suspension of lithium aluminum deuteride (1.6 g) in dry ether (80 ml). The reaction mixture is heated under reflux for... 

The saturation of linear dienones provides a means of labeling even more remote sites. Labeling of the C-2 and C-3 positions of androstan-7-... 

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