Vitamin D receptor activators and methods of making

1. A compound of formula (I):

or a pharmaceutically acceptable salt thereof, wherein

the carbon to which X is attached can have the R or S configuration;

X is —CH 2 OC(O)R 2 ;

Y 1 and Y 2 are each hydrogen;

Y 3 and Y 4 taken together are a methylene group;

Z 1 is fluorine, hydroxy, or hydroxymethyl;

Z 2 is fluorine or hydroxy; and

R 2 is alkyl, alkylamino, alkylcarbonyloxyalkyl, or hydroxyalkyl.

2. A compound of claim 1 , wherein

X is —CH 2 OC(O)R 2 ;

Y 1 and Y 2 are each hydrogen;

Y 3 and Y 4 taken together are a methylene group;

Z 1 is hydroxy;

Z 2 is hydroxy; and

R 2 is alkyl, alkylamino, alkylcarbonyloxyalkyl, or hydroxyalkyl.

3. A compound of claim 2 , wherein

X is —CH 2 OC(O)R 2 ;

Y 1 and Y 2 are each hydrogen;

Y 3 and Y 4 taken together are a methylene group;

Z 1 is hydroxy;

Z 2 is hydroxy; and

R 2 is alkyl.

4. A compound of formula (I) as in claim 1 that is:

(2S)-2-[(1R,3R,7E, 17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl pivalate;

(2R)-2-[(1R,3R,7E,17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl pivalate;

(2S)-2-[(1R,3R,7E,17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl 2,2-dimethylbutanoate;

(2S)-2-[(1R,3R,7E,17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl tert-butylcarbamate;

(2S)-2-[(1R,3R,7E,17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl 2-(acetyloxy)-2-methylpropanoate;

(2S)-2-[(1R,3R,7E,17β)-1,3-dihydroxy-2-methylene-9,10-secoestra-5,7-dien-17-yl]propyl 2-hydroxy-2-methylpropanoate;

or a pharmaceutically acceptable salt thereof.

5. A pharmaceutical composition comprising a therapeutically effective amount of a compound of claim 1 , or a salt thereof, in a pharmaceutically acceptable carrier.