Synthesis, Optical Rotation, and Absolute Configurations of Santinols

Abstract

Santinols A1 and A2, two of the asymmetric 1,3-diacylglycerols (1,3-diacylglycerides) recently isolated from Helichrysum italicum subsp. microphyllum, were synthesized for the first time. The synthetic samples showed essentially the same 1 H and 13 C NMR spectra as reported for natural santinols. The optical rotations were also consistent with those for their natural counterparts, but only for less than an hour after the preparation of the sample solution; the sign of the optical rotation may reverse after a more prolonged time, revealing

Enantioselective Synthesis of the Proposed Structure of Santinol D

“…Our previous [2,3] studies have verified that santinols A and C possess an (S) configuration at the C-2. Therefore, it is reasona- [a] Synthesis of (2′′′S,4′′′R)-5 [9] was carried as shown in Scheme 2.…”

“…A colorless oil (10.856 g, 39.77 mmol, 62 %; chromatography using 10:1 PE/EtOAc). [ α ] D 25 = –38.7 ( c = 1.0, CHCl 3 ) {ref [ α ] D 19 = –39.0 ( c = 1.0, CHCl 3 )}. 1 H NMR (400 MHz, CDCl 3 ) δ = 7.36–7.26 (m, 3H), 7.24–7.19 (m, 2H), 5.83 (ddt, J = 17.1, 10.1, 7.0 Hz, 1H), 5.15–5.03 (m, 2H), 4.72–4.64 (m, 1H), 4.22–4.12 (m, 2H), 3.86 (sext, J = 6.8 Hz, 1H), 3.28 (dd, J = 13.3, 3.3 Hz, 1H), 2.70 (dd, J = 13.3, 9.8 Hz, 1H), 2.58–2.47 (m, 1H), 2.29–2.19 (m, 1H), 1.19 (d, J = 6.8 Hz, 3H) ppm; 13 C NMR (100 MHz, CDCl 3 ) δ = 176.58, 153.20, 135.46, 135.35, 129.50, 129.01, 127.39, 117.30, 66.09, 55.46, 38.17, 38.06, 37.23, 16.51 ppm.…”

“…The resulting alcohols were converted into the corresponding aldehydes (10 [7] or ent-10, respectively) cleanly by Swern [8] oxidation and then directly employed in the next step without any purification (to minimize any possible racemization). The benzyl protecting group was removed by hydrogenolysis over Pearlman [12] catalyst [Pd(OH) 2 ]. The resulting diol 16 was then acylated with 17 under the conditions similar to those for the conversion of 13 into 15.…”

Racemization of α‐Alkyl‐β‐Keto Esters and Enantioselective Total Synthesis of Two C‐2′′′Epimers of Plant Glycerolipid Santinol C

“…Our synthesis of (2 S ,2′′′ S )‐ 5 is outlined in Scheme : reaction of 14 with EtCO 2 H gave 15 , which on hydrolysis and acylation with 7 afforded 17 . Debenzylation followed by acylation with angelic acid provided 19 .…”

Finding reliable methodology for optical rotation and correct predictions of (s)‐methyloxirane and (1R,5R)‐β‐pinene

“…plane-polarized light deviation after passing the sample with enantiomeric excess 6 and has a wide range of applications from solid state research 7,8 to natural products. [9][10][11] The OR value of a substance is dependent to wavelength of incident radiation and signs are opposite for enantiomers.…”