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DOI: 10.1055/s-2005-871927
A Short Stereoselective Synthesis of (R)-Salmeterol
Publication History
Publication Date:
07 July 2005 (online)
Abstract
A short, highly stereoselective oxy-Michael approach to the total synthesis of the β2-agonist, (R)-salmeterol is described.
Key words
asymmetric synthesis - oxy-Michael addition - 1,2-amino alcohol - δ-lactol
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References
Data for synthetic 1: [α]D 25 -21.1 (c 1.48, CHCl3), [lit. [6] [α]D 25 -20.6 (c 1.46, CHCl3)]. 1H NMR (400 MHz, CD3OD, lit. [5c] ): δ = 7.29 (1 H, s, Ar-CH), 7.23 (2 H, m, Ar-CH), 7.17-7.11 (4 H, m, Ar-CH), 6.75 (1 H, d, J = 8.1 Hz, Ar-CH), 4.68 (1 H, dd, J = 8.7, 4.2 Hz, CHCH2NH), 4.65 (2 H, s, CH 2OH), 3.44-3.39 (4 H, m, CH 2OCH 2), 3.35 (1 H, s, NH), 3.31 (2 H, s, 2 × OH), 2.77 (1 H, dd, J = 12.1, 8.8 Hz, CHCHHNH), 2.71 (1 H, dd, J = 12.1, 4.3 Hz, CHCHHNH), 2.61 (4 H, m, J = 6.8 Hz, CH2CH 2Ph and NHCH 2CH2), 1.71-1.56 (8 H, m, 4 × CH2), 1.37-1.29 (4 H, m, 2 × CH2). 13C NMR (100 MHz, CD3OD): δ = 154.5 (OAr-1), 142.3 (Ar), 133.6 (Ar), 128.1 (Ar), 128.0 (Ar), 127.9 (Ar), 127.1 (Ar), 125.7 (Ar), 125.3 (Ar), 114.5 (Ar-5), 71.6 (CHCH2NH), 70.4 (CH2 °CH2), 70.3 (CH2OCH2), 59.7 (ArCH2), 56.4 (CHCH2NH), 50.2 (NHCH2CH2), 35.2 (CH2 CH2Ph), 30.3 (CH2), 29.2 (CH2), 28.9 (CH2), 27.9 (CH2), 26.7 (CH2), 25.7 (CH2). IR (film): νmax = 3675 (OH), 2987, 2901, 1452, 1406, 1394 cm-1. HRMS (ES+): m/z calcd for C25H38NO4 [M + H]+: 416.2795; found: 416.2796. Chiral HPLC was performed on a Sumichiral OA-4100 column (25 cm × 4.6 mm) eluting with hexane-EtOH-CH2Cl2-TFA (240:30:130:1), at a flow rate of 1 mL/min, detecting at 276 nm; t R = 19.26 min, 2.0% [S-isomer]; t R = 21.84 min, 98.0% [R-isomer].