Jaap van der Louw

Q) SAR study on the metabolic stability of steroidal androgens.

Metabolic stability is a key issue in the development of orally active androgens for Partial Androgen Deficiency in Aging Males (PADAM) and male contraception. Rates of metabolism in human hepatocyte suspensions provide useful information on the stability of compounds that undergo a first pass metabolism. We have derived a structure-pharmacokinetic relationship for a data set of 32 in-house steroidal androgens by means of the decision-trees technique. Volume, shape, number of rotatable bonds, and surface turned out to be the most important descriptors for classification. Only 2 of the 32 compounds were misclassified. The most stable compounds were classified in three leaf nodes on different branches of the tree, suggesting that higher metabolic stability can be achieved for the same substrate by different steric modifications. Further, it is generally assumed that the first step in cytochrome P450s oxidation reactions takes place by hydrogen abstraction to form a radical intermediate. An electronic model for hydrogen abstraction in steroidal androgens was, therefore, developed by means of ab initio calculations. Activation energies of steroid radical systems calculated as energy differences between the reactants equilibrium geometry energies and their corresponding transition states energies could be used to predict relative rates of metabolism to guide the design and redesign process of metabolically more stable steroidal androgens.

The synthesis of functionalized 13,14-seco-steroids via Grob fragmentation

A synthetic methodology for the synthesis of 13,14-seco-steroids with substituents at C-14 and C-17 is described. The approach involves Grob fragmentation of 14beta-hydroxy-17beta-tosylates, hydroboration-oxidation of the intermediate delta13(17)-olefin, and hydride reduction of the 14-ketone. An unambiguous structural assignment of (13R,14S,17S)-14,17-diacetoxy-3-methoxy-7alpha-methyl-13,14-secoestra-1,3,5(10)-triene was determined by X-ray analysis.

Structure–activity relationship study of human liver microsomes-catalyzed hydrolysis rate of ester prodrugs of MENT by comparative molecular field analysis (CoMFA)

A series of MENT esters (3-71) was designed, prepared and tested to study the structure-activity relationship (SAR) of the hydrolysis rate with human liver microsomes of these prodrugs. Compounds were obtained covering a wide range of metabolic stability. The results are useful for the proper selection of prodrugs for different pharmaceutical formulations to deliver the potent and prostate-sparing androgen MENT. The MENT esters can especially be administered for male hormone replacement therapy and male contraception. Comparative molecular field analysis (CoMFA) was applied to a dataset of 28 esters, for which ED50 values could be obtained. The CoMFA model where the electrostatic and H-bond molecular fields were combined turned out to be most predictive. Despite the limited size of the dataset, CoMFA can help to rationalize the SAR of the ester hydrolysis rate of ester prodrugs of MENT.

Reaction of (13S)-13-iodo-6beta-methoxy-3alpha,5-cyclo-13,14-seco-5alpha-androstane-14,17-dione with hydroxylamine and its application to the synthesis of new 13,14-seco steroids.

The synthesis of 13,14-seco steroids starting from easily available (13S)-13-iodo-6-methoxy-3,5-cyclo-13,14-seco-5-androsta-14,17-dione is described. The C-17 ketone was converted regioselectively into its oxime with simultaneous stereoselective deiodination at C-13. The remaining C-14 carbonyl group was then reduced stereoselectively with Ca(BH4)2. The configurations at the relevant stereocenters of the thus obtained hydroxy oxime were determined by X-ray analysis. Successful regeneration of the C-17 carbonyl group was achieved by treatment of the corresponding oxime acetate with TiCl3.

Synthesis of 13,14-secotestosterone derivatives

A number of testosterone analogs with a 13,14-secosteroidal fragment have been prepared from (13S)-13-iodo-6beta-methoxy-3alpha, 5-cyclo-13,14-seco-5alpha-androstan-14,17-dione. The key steps involved stereoselective deiodination of the starting compound with triphenylphosphine and selective protection of the 17-keto group with trimethylsilylcyanide. Removal of iodine at C-13 proceeded with inversion of the configuration at C-13, which has been established by X-ray crystallography. 13,14-Secotestosterone analogues substituted and non-substituted at C-14 have been prepared. The obtained compounds containing flexible CD ring fragments are of great interest for comparative studies in biological tests together with testosterone and other steroids with a rigid tetracyclic skeleton.

Isolation and structure elucidation of new radical oxidation products of 5-hydroxy steroids

Three new products have been isolated from the lead-tetraacetate version of the hypoiodite oxidation of 3beta,17beta-diacetoxy-5-hydroxy-5 alpha-androstane. Along with the expected 1(10)-unsaturated 5,10-seco steroidal 5-ketones, the fragmentation reaction gave two epimeric C-4 iodides. Their structural assignment was based on X-ray data of one of them ((4R,10S)-4-iodo-3beta,17beta-diacetoxy-5,10-secoandrostan-5-one). The third new product was found to be the 5 beta,6 beta-epoxide resulting from the dehydration of the tertiary alcohol followed by epoxidation of the intermediate Delta(5)-olefin.

A new type of steroids with a cyclobutane fragment in the AB-ring moiety

The synthesis of a 5,10-seco steroid containing two double bonds in a AB-macrocycle as well as the preparation of a steroidal skeleton with a cyclobutane fragment is described. The structures of these compounds are different from those of natural steroids, but they are very similar with respect to conformation of the carbon skeleton.

Calculated heats of formation of sterol diene isomers compared with synthetic yields of isomerisation reactions of Δ5,7 sterols

Heats of formation of five series of diene sterol isomers were calculated and compared with synthetic yields of acid-catalysed isomerisation reactions starting from Δ5,7 isomers. Calculations were based on molecular mechanics, using the MM3 program package. For each of the five Δ5,7 starting compounds, three possible reaction paths were considered, in which heats of formation were calculated for theoretically possible intermediate double bond isomers. Similar results are found for all five series. The starting compounds are found to have the unfavourable heats of formation compared to all other isomers considered within one series. In general, isomerisation reactions of diene sterols ultimately yield spiro compounds when allowed to proceed for a sufficient amount of time. These compounds are found to have the lowest heats of formation in each series. However, they were not formed in the reactions considered in this paper, because the reactions were stopped after the desired isomer was formed in excess, before the spiro compounds could occur. Most compounds identified as products in the syntheses have a favourable heat of formation compared to the isomers preceding the (most stable) spiro compounds. However, when the reactions were carried out at low temperature, isomers with less favourable heats of formation could be trapped. We show that calculated heats of formation correspond well with synthetic yields and we suggest they can be a useful tool in planning syntheses.

Synthesis of 5,10-seco analogs of testosterone

A number of 5,10-seco analogs of testosterone has been synthesized starting from products of the radical oxidation of 3beta,17beta-diacetoxy-5alpha-androstan-5alpha-ol. The obtained compounds possess a flexible 10-membered ring with substituents (O, -OH) at C-3 and C-5. Similar derivatives with an (E)- and (Z)-Delta(1(10))-double bond have been prepared also. X-ray analysis and a combination of NMR experiments have been used for their structure elucidation and conformation analysis.