Treatment of Pulmonary Disease

1 . A method of treating or alleviating a pulmonary disease or condition caused by or associated with narrowing of the pulmonary blood vessels in a subject, comprising administering to the subject a therapeutically effective amount of a compound of formula A:

or a pharmaceutically acceptable salt thereof, wherein:

R 1 is hydrogen or unsubstituted C 1 -C 6 alkyl;

R 2 is hydrogen or α-hydroxyl;

X is C(O)OH, C(O)NH(CH 2 ) m SO 3 H, or C(O)NH(CH 2 ) n CO 2 H;

R 4 is hydroxyl or hydrogen;

R 7 is hydroxyl or hydrogen;

m is an integer 1, 2, or 3; and

n is an integer 1, 2, or 3.

2 . The method of claim 1 , wherein R 1 is unsubstituted C 1 -C 6 alkyl.

3 . The method of claim 2 , wherein R 1 is methyl, ethyl, or propyl.

4 . The method of claim 3 , wherein R 1 is ethyl.

5 . The method of claim 1 , wherein R 1 is selected from methyl, ethyl and propyl; R 4 is OH; R 7 is H; and R 2 is H.

6 . The method of claim 1 , wherein the compound is

or a pharmaceutically acceptable salt thereof.

7 . The method of claim 1 , wherein the pulmonary disease or condition is selected from obstructive pulmonary disease (COPD), emphysema, asthma, idiopathic pulmonary fibrosis, pneumonia, tuberculosis, cystic fibrosis, bronchitis, pulmonary hypertension, Primary Pulmonary Hypertension (PPH), Secondary Pulmonary Hypertension (SPH), interstitial lung disease, and lung cancer.

8 . The method of claim 7 , wherein the pulmonary disease or condition is selected from COPD, emphysema, asthma, cystic fibrosis, and pulmonary hypertension.

9 . The method of claim 8 , wherein the pulmonary disease or condition is pulmonary hypertension.

10 . The method of claim 9 , wherein the pulmonary hypertension is idiopathic pulmonary arterial hypertension (IPAH) or secondary pulmonary hypertension (SPH).

11 . The method of claim 1 , wherein the subject is a human.

12 . The method of claim 1 , wherein the compound is administered systemically, orally, intravenously, intramuscularly, intraperitoneally, or by inhalation.