Are you thinking of 3,4-Dimethylaminorex or the simple 3-Methylaminorex?
As far as I know, the N-methylated homologs are more toxic and less active (with N-methylation, you lock the imine/amine tautomerism):
Post 354971 (https://www.thevespiary.org/talk/index.php?topic=9285.msg35497100#msg35497100)
(Rhodium: "PPA synthetic routes + 3,4-DMAR Note", Methods Discourse)
Post 233539 (https://www.thevespiary.org/talk/index.php?topic=11418.msg23353900#msg23353900)
(psychokitty: "Re: Mechanism", Novel Discourse)
The following paper doesn't state anything about 4-fluoroaminorex potency but does give the relative potency of p-chloro and p-fluoro aminorex as 2x and 4x that of aminorex, respectively.
http://www.streamload.com/scarmani/Poos_2-amino-5-Aryl-2-oxazolines._Potent_New_Anorectic_Agents.pdf (http://www.streamload.com/scarmani/Poos_2-amino-5-Aryl-2-oxazolines._Potent_New_Anorectic_Agents.pdf)
"...A series of 2-amino-5-aryl-2-oxazolines was found to have potent appetite suppressant activity. Methods of synthesis, chemical behavior, and structure-activity relationships for these compounds are described..."
It also gives the possible authors for that more extensive paper mentioned above (aminorex-analog-activities as tested in lab rats.)
"As in the case for anorectic activity, the CNS and cardiovascular effects of these aminooxazolines were found to vary significantly with changes in structure. The results of these studies will be reported elsewhere in detail... [J. F. Gardocki and J. Yelnosky, manuscript in preparation.] ... The anorectic activity found for several of these compounds in rats has been substatiated in human beings."
a large clump of other PDF's (oxazoline / anorexigenic related) with varying degrees of relevance is here:
http://www.streamload.com/scarmani/ (http://www.streamload.com/scarmani/)