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RTI-113
Identifiers
	IUPAC name Phenyl (2S,3S)-3-(4-chlorophenyl)-8-methyl-8-azabicyclo[3.2.1]octane-2-carboxylate;
CAS Number	146145-17-7 ; HCl: 141807-57-0 ;
PubChem CID	9886801;
ChemSpider	8062474 ;
ChEMBL	ChEMBL608548 ;
CompTox Dashboard (EPA)	DTXSID301028557 ;
Chemical and physical data
Formula	C21H22ClNO2
Molar mass	355.86 g·mol−1
3D model (JSmol)	Interactive image;
	SMILES CN1C2CCC1[C@H]([C@H](C2)C3=CC=C(C=C3)Cl)C(=O)OC4=CC=CC=C4;
	InChI InChI=1S/C21H22ClNO2/c1-23-16-11-12-19(23)20(21(24)25-17-5-3-2-4-6-17)18(13-16)14-7-9-15(22)10-8-14/h2-10,16,18-20H,11-13H2,1H3/t16?,18-,19?,20+/m1/s1 ; Key:AAEKULYONKUBOZ-MLFFRYNPSA-N ;
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RTI(-4229)-113 (2β-carbophenoxy-3β-(4-chlorophenyl)tropane) is a stimulant drug which acts as a potent and fully selective dopamine reuptake inhibitor (DRI). It has been suggested as a possible substitute drug for the treatment of cocaine addiction. "RTI-113 has properties that make it an ideal medication for cocaine abusers, such as an equivalent efficacy, a higher potency, and a longer duration of action as compared to cocaine."^[1] Replacing the methyl ester in RTI-31 with a phenyl ester makes the resultant RTI-113 fully DAT specific. RTI-113 is a particularly relevant phenyltropane cocaine analog that has been tested on squirrel monkeys.^[2] RTI-113 has also been tested against cocaine in self-administration studies for DAT occupancy by PET on awake rhesus monkeys.^[3] The efficacy of cocaine analogs to elicit self-administration is closely related to the rate at which they are administered.^[4] Slower onset of action analogs are less likely to function as positive reinforcers than analogues that have a faster rate of onset.^[4]^[5]

In order for a DRI such as cocaine to induce euphoria PET scans on primates reveal that the DAT occupancy needs to be >60%.^[6] Limited reinforcement may be desirable because it can help with patient compliance. DAT occupancy was between 65-76% and 94-99% for doses of cocaine and RTI-113 that maintained maximum response rates, respectively.^[3] Whereas cocaine is a fast acting rapidly metabolized DRI, RTI-113 has a longer duration span.^[7]

Self-administration graphs are inverted U-shaped. More doses of cocaine need to be administered per session than for RTI-113 because cocaine doesn't last as long as RTI-113 does. It is easy to form the rash judgement that the NRI and SRI properties of cocaine are somehow having an additive effect on provoking self-administration of cocaine.^[8]

Although NRIs are known to inhibit DA reuptake in the prefrontal cortex where DATs are low in number, the fact that desipramine is not reliably self-administered makes it unlikely that NRIs are contributing to the addictive character of cocaine.^[9]

The 5-HT receptors are very complex to understand and can either mediate or inhibit DA release.

However, on the whole, it is understood that synaptic 5-HT counterbalances catecholamine release.

Thus, it can said with relative certainty that the DAT is responsible for the bulk of the reinforcing effects of cocaine and related stimulants.^[10]

With regard to amphetamine, a recent paper disputes this claim, and makes the point that the role of NE is completely underrated.^[11]

Another paper was also recently published, seeking to address the relevance of NE in cocaine pharmacology.^[12]

Transporter Selectivity

MAT IC₅₀ (and K_i) for simple phenyltropanes with 1R,2S,3S stereochemistry.^[13]
Compound	[³H]CFT	[³H]DA	[³H]Nisoxetine	[³H]NE	[³H]Paroxetine	[³H]5-HT
Cocaine^[14]	89.1	275 cf. 241	3300 (1990)	119 cf. 161	1050 (45)	177 cf. 112
Troparil	23	49.8	920 (550)	37.2	1960 (178)	173
WIN 35428	13.9	23.0	835 (503)	38.6	692 (63)	101
RTI-31	1.1	3.68	37 (22)	5.86	44.5 (4.0)	5.00
RTI-113^[15]	1.98	5.25	2,926	242	2,340	391
RTI-51	1.7	?	37.4 (23)	?	10.6 (0.96)	?
RTI-55	1.3	1.96	36 (22)	7.51	4.21 (0.38)	1.74
RTI-32	1.7	7.02	60 (36)	8.42	240 (23)	19.4

Note: cocaine has a very strong Ki value for the 5-HT₃ receptor.

Threo-methylphenidate is a weaker dopaminergic than troparil, even though it is a more potent noradrenergic.

Troparil is the only tropane in the above table having a [³H]NE figure that is smaller than the [³H]DA number.

References

^ Kimmel HL, Carroll FI, Kuhar MJ (December 2001). "Locomotor stimulant effects of novel phenyltropanes in the mouse". Drug and Alcohol Dependence. 65 (1): 25–36. doi:10.1016/S0376-8716(01)00144-2. PMID 11714587.
^ Howell LL, Czoty PW, Kuhar MJ, Carrol FI (February 2000). "Comparative behavioral pharmacology of cocaine and the selective dopamine uptake inhibitor RTI-113 in the squirrel monkey". The Journal of Pharmacology and Experimental Therapeutics. 292 (2): 521–529. PMID 10640288.
^ ^a ^b Wilcox KM, Lindsey KP, Votaw JR, Goodman MM, Martarello L, Carroll FI, Howell LL (January 2002). "Self-administration of cocaine and the cocaine analog RTI-113: relationship to dopamine transporter occupancy determined by PET neuroimaging in rhesus monkeys". Synapse. 43 (1): 78–85. CiteSeerX 10.1.1.555.2703. doi:10.1002/syn.10018. PMID 11746736. S2CID 26487942.
^ ^a ^b Kimmel HL, Negus SS, Wilcox KM, Ewing SB, Stehouwer J, Goodman MM, et al. (September 2008). "Relationship between rate of drug uptake in brain and behavioral pharmacology of monoamine transporter inhibitors in rhesus monkeys". Pharmacology, Biochemistry, and Behavior. 90 (3): 453–462. doi:10.1016/j.pbb.2008.03.032. PMC 2453312. PMID 18468667.
^ Wee S, Carroll FI, Woolverton WL (February 2006). "A reduced rate of in vivo dopamine transporter binding is associated with lower relative reinforcing efficacy of stimulants". Neuropsychopharmacology. 31 (2): 351–362. doi:10.1038/sj.npp.1300795. PMID 15957006.
^ Howell LL, Wilcox KM (July 2001). "The dopamine transporter and cocaine medication development: drug self-administration in nonhuman primates" (PDF). The Journal of Pharmacology and Experimental Therapeutics. 298 (1): 1–6. PMID 11408518. Archived from the original (PDF) on 2006-09-21.
^ Cook CD, Carroll FI, Beardsley PM (May 2002). "RTI 113, a 3-phenyltropane analog, produces long-lasting cocaine-like discriminative stimulus effects in rats and squirrel monkeys". European Journal of Pharmacology. 442 (1–2): 93–98. doi:10.1016/S0014-2999(02)01501-7. PMID 12020686.
^ Rocha BA, Fumagalli F, Gainetdinov RR, Jones SR, Ator R, Giros B, et al. (June 1998). "Cocaine self-administration in dopamine-transporter knockout mice". Nature Neuroscience. 1 (2): 132–137. doi:10.1038/381. PMID 10195128. S2CID 20444986.
^ Gasior M, Bergman J, Kallman MJ, Paronis CA (April 2005). "Evaluation of the reinforcing effects of monoamine reuptake inhibitors under a concurrent schedule of food and i.v. drug delivery in rhesus monkeys". Neuropsychopharmacology. 30 (4): 758–764. doi:10.1038/sj.npp.1300593. PMID 15526000.
^ Chen R, Tilley MR, Wei H, Zhou F, Zhou FM, Ching S, et al. (June 2006). "Abolished cocaine reward in mice with a cocaine-insensitive dopamine transporter". Proceedings of the National Academy of Sciences of the United States of America. 103 (24): 9333–9338. Bibcode:2006PNAS..103.9333C. doi:10.1073/pnas.0600905103. PMC 1482610. PMID 16754872.
^ Sofuoglu M, Sewell RA (April 2009). "Norepinephrine and stimulant addiction". Addiction Biology. 14 (2): 119–129. doi:10.1111/j.1369-1600.2008.00138.x. PMC 2657197. PMID 18811678.
^ Platt DM, Rowlett JK, Spealman RD (August 2007). "Noradrenergic mechanisms in cocaine-induced reinstatement of drug seeking in squirrel monkeys". The Journal of Pharmacology and Experimental Therapeutics. 322 (2): 894–902. doi:10.1124/jpet.107.121806. PMID 17505018. S2CID 10100028.
^ Carroll FI, Kotian P, Dehghani A, Gray JL, Kuzemko MA, Parham KA, et al. (January 1995). "Cocaine and 3 beta-(4'-substituted phenyl)tropane-2 beta-carboxylic acid ester and amide analogues. New high-affinity and selective compounds for the dopamine transporter". Journal of Medicinal Chemistry. 38 (2): 379–388. doi:10.1021/jm00002a020. PMID 7830281.
^ Kozikowski AP, Johnson KM, Deschaux O, Bandyopadhyay BC, Araldi GL, Carmona G, et al. (April 2003). "Mixed cocaine agonist/antagonist properties of (+)-methyl 4beta-(4-chlorophenyl)-1-methylpiperidine-3alpha-carboxylate, a piperidine-based analog of cocaine". The Journal of Pharmacology and Experimental Therapeutics. 305 (1): 143–150. doi:10.1124/jpet.102.046318. PMID 12649362. S2CID 29377097.
^ Damaj MI, Slemmer JE, Carroll FI, Martin BR (June 1999). "Pharmacological characterization of nicotine's interaction with cocaine and cocaine analogs". The Journal of Pharmacology and Experimental Therapeutics. 289 (3): 1229–1236. PMID 10336510.