@article{5f2156a1910d4742b247252ffa80350a,
title = "Relative configuration of the diacid sidechain of isoharringtonine",
author = "Touran Ipaktchi and Weinreb, \{Steven M.\}",
note = "Funding Information: proton at 6.80 6 in the nmr (vs 6.68 6 for that of dimethyl mesaconate6). Hydroxylation of 7 with osmium tetroxide/hydrogen peroxide in t-butanol at 50° for 48 hrs produced ffsingle diol 3 (65°B:7 m.p. 55-56'; ir (CHC13) 3500, 1740 cm-1; nmr (CDC13) 6 0.88 (6H,d,J = 6 Hz)f;.O-2.0 (SH,m), 3.52 (lH, d,J = 8 Hz, OH), 3.70 (lH,s,OH), 3.80 (6H s), 4.32 (lH, d, J = 8 Hz, collapses to a singlet on D20 shaking). It is well established that hydroxylation with this combination of reagents gives the cis stereochemistry of the resulting diol. Thus diethyl fumarate and diethyl maleate yield dl and meso tartaric acid esters respectively.8 Dehydration of diacidi with phosphorous pentoxide affords anhydride 8: ir (film) 1830, 1775 cm -1 . Conversion of z to diester 2 was effected by hea?ing with methanol/sulfuric acid. Diester 9 has its vinyl proton upfield relative to that of 7 at 5.85 6 in the nmr (vs 5.77 6 fzr that of dimethyl citraconate'), Hydroxylation of*9 with osmium tetroxide/hydrogen peroxide in t-butanol at 50' for 48 hrs again produced* a single diol, 2 (40\%)? m.p. 70-72'; ir (CHC13) 3500, 1740 cm -1 ; nmr (CDC13) 6 0.88 (6H,d J = 6 Hz), l-O-2.1 (SH, m), 3.25 (lH,d,J = 8 Hz,OH), 3.42 (lH,s,OH), 3.76 (3H,s), 3.82 (3H,s), 4.41 (lH,d, J = 8 Hz, collapses to a singlet on D20 shaking). Comparison of the nmr spectra of 2 and 2 with that of the transesterification product of isoharringtonine 2b,e,9 clearly shows the natural isomer to be identical, except for optical activity, to the erythro isomer 4. Still unknown however are the absolute confi\&ations of both cephalotaxine (1) and the diacid portion of isoharringtonine. We are currently investigating this przblc Acknowledgement: This work was supported by grants from The National (CA 12568), the Research Corporation, and Hoffmann-LaRoche. We also continuing exchange of information with Mr. R.G. Powell.",
year = "1973",
doi = "10.1016/S0040-4039(01)87066-0",
language = "English (US)",
volume = "14",
pages = "3895--3898",
journal = "Tetrahedron Letters",
issn = "0040-4039",
publisher = "Elsevier Ltd",
number = "40",
}