Abstract: Piperazine derivatives of the formula ##STR1## their esters and salts are useful as modulators of multiple drug resistance.

Abstract: Piperazine derivatives of formula (A): ##STR1## wherein .sub.-------- denotes an optional bond, provided that either .sub.----.sup.a.sub.---- and .sub.----.sup.c.sub.---- are both bonds and .sub.----.sup.b.sub.---- and .sub.----.sup.d.sub.---- are not bonds, or .sub.----.sup.b.sub.---- and .sub.----.sup.d.sub.---- are both bonds and .sub.----.sup.a.sub.---- and .sub.----.sup.c.sub.---- are not bonds; each of R.sub.14 and R.sub.15 is independently selected from hydrogen and C.sub.1 -C.sub.6 alkyl which is unsubstituted or substituted by an organic functional group; and each of R.sub.1 to R.sub.10, which may be the same or different, is independently hydrogen or an organic functional group; and the pharmaceutically acceptable salts and esters thereof have utility as modulators of multiple drug resistance (MDR).

Abstract: A diketopiperazine of formula (I): ##STR1## wherein each of R.sub.7 and R.sub.8 which may be the same or different; is hydrogen or a nitro group;Y is ##STR2## --O-- or --S--, wherein each of R.sub.9 and R.sub.10 which may be the same or different, is hydrogen or a nitro group;n is 0, 1 or 2;m is an integer of 1 to 6;each R.sub.6, which may be the same or different, is a C.sub.1 -C.sub.6 alkyl group; andX is selected from(i) a phenyl group of the following formula ##STR3## and the salts and esters thereof; have activity as inhibitors of plasminogen activator inhibitor.

Abstract: Diketopiperazines of the formula: ##STR1## where each of R.sub.1 to R.sub.10, which may be the same or different, is independently selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl unsubstituted or substituted by one or more halogen atoms, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, halogen, hydroxy, nitro, phenyl, -cyano, --CH.sub.2 OH, --CH.sub.2 COOH, --CO.sub.2 R.sup.11, --NHCOR.sup.11, --NHSO.sub.2 R.sup.13, --SO.sub.2 R.sup.13, --CON(R.sup.11 R.sup.12), --SOR.sup.13, --SO.sub.2 N(R.sup.11 R.sup.12), --N(R.sup.11 R.sup.12), and --O(CH.sub.2).sub.n N(R.sup.11 R.sup.12), --O(CH.sub.2).sub.n CO.sub.2 R.sup.11, --OCOR.sup.11, --CH.sub.2 OCOR.sup.11, --CH.sub.2 NHCOR.sup.11, --CH.sub.2 NHCOOR.sup.13, --CH.sub.2 SR.sup.11, --CH.sub.2 SCOR.sup.11, --CH.sub.2 S(O).sub.m R.sup.13 wherein m is 1 or 2, --CH.sub.2 NHCO(CH.sub.2).sub.n CO.sub.2 R.sup.11, --N(R.sup.11)COR.sup.12, --NHCOCF.sub.3, --NHCO(CH.sub.2).sub.n CO.sub.2 R.sup.11, --NHCO(CH.sub.2).sub.n OCOR.sup.11 and --NHCO(CH.