beta-Oxygenated Analogues of the 5-HT2A Serotonin Receptor Agonist 1-(4-Bromo-2,5-dimethoxyphenyl)-2-aminopropaneRichard A. Glennon, Mikhail L. Bondarev, Nantaka Khorana, Richard Young, Jesse A. May, Mark R. Hellberg, Marsha A. McLaughlin, and Najam A. SharifJ. Med. Chem., 2004, ASAP Web Release Date: 16-Oct-2004DOI:
10.1021/jm040082s
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Abstract: Activation of 5-HT
2A serotonin receptors represents a novel approach to lowering intraocular pressure. Because 5-HT
2A serotonin receptor agonists might also produce undesirable central effects should sufficient quantities enter the brain, attempts were made to identify 5-HT
2 serotonin receptor agonists with reduced propensity to penetrate the blood-brain barrier. 1-(4- Bromo-2,5-dimethoxyphenyl)-2-aminopropan-1-ol (
6), an analogue of the 5-HT
2 serotonin receptor agonist 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB;
1a) bearing a benzylic hydroxyl group, was identified as a candidate structure. Of the four optical isomers of
6, the 1R,2R-isomer (
6d; K
i = 0.5 nM) was found to bind at 5-HT
2A receptors with an affinity similar to that of R(-)DOB (K
i = 0.2 nM). Like R(-)DOB,
6d behaved as a partial agonist (efficacy ca. 50%) in a 5-HT
2-mediated calcium mobilization assay. However, in an in vivo test of central action (i.e., stimulus generalization with rats as subjects),
6d was >15 times less potent than R (-)DOB. O-Methylation of
6d (i.e.,
7d; 5-HT
2A K
i = 0.3 nM) resulted in an agent that behaved as a full (93% efficacy) agonist. Intraocular administration of 300 µg of
6d and
7d to ocular hypertensive monkeys was shown to reduce intraocular pressure by 20-27%. Given the route of administration (i.e., topical), and concentrations necessary to reduce intraocular pressure, compounds such as
6d should demonstrate minimal central effects at potentially useful therapeutic doses and offer useful leads for further development.
Scheme 1 Reagents and conditions: (a) Br
2/CHCl
3, 5 °C to room temperature, 2 h; (b) (CH
2)
6N
4/CHCl
3, 50 °C, 1 h, then HCl/EtOH, 50 °C, 3 h; (c) NaBH
4/MeOH, 0 °C; (d) ClCH
2COCl/NaOH/H
2O/CH
2Cl
2, 0 °C to room temperature, 2 h; (e) KOH/EtOH, 12 h, room temperature; (f) BH
3-THF, reflux, 12 h.
Scheme 2 Reagents and conditions: (a) (COCl)
2/CH
2Cl
2, 1-bromo-2,5-dimethoxybenzene/TiCl
4, -50 C to room temperature, 60 h; (b) SiH(CH
3)2Ph/TFA, -5 °C, 2 h then K
2CO
3, reflux, 2 h; (c) Ac
2O, room temperature to 110 °C, 1 h, then 60% H
2SO
4, 110 °C, 1 h; (d) NaH/THF, 0 °C to room temperature 0.5 h, then MeI, reflux, 1 h.