The invention relates to the use of compounds of formula (I):
wherein X is —C(O)—, —C(S)—, —C═NOH, or —CH(R
7
)— wherein R
7
is hydrogen, hydroxy, C
1-7
alkoxy, —OR
8
or —NR
8
R
9
(wherein R
8
is a group —Y
1
R
10
(wherein Y
1
is a direct bond, —C(O)—, —C(S)—, —S—, —C(O)O—, —C(O)NR
11
—, —SO
2
— or —SO
2
NR
12
— (wherein R
11
and R
12
, which may be the same or different, each independently represents hydrogen; C
1-3
alkyl or C
1-3
alkoxyC
2-3
alkyl) and R
10
is as defined herein, R
9
includes hydrogen; R
11
, R
12
and R
13
are as defined herein and are preferably methyl; R
4
, R
5
and R
6
are as defined herein with the proviso that R
5
is not hydroxy, alkoxy, substituted alkoxy, —OPO
3
H
2
, —O—C
1-7
alkanoyl or benzyloxy; and salts thereof in the manufacture of a medicament for use in the production of a vascular damaging effect in warm-blooded animals such as humans. The present invention further relates to compounds of the formula (I), pharmaceutical compositions containing them, processes for their preparation and to a method of treatment using the compounds to produce a vascular damaging effect in a warm-blooded animal such as a human. The compounds of formula (I) and the pharmaceutically acceptable salts thereof may be useful in the treatment of a number of disease states including cancer and rheumatoid arthritis.