𝔖 Bobbio Scriptorium
✦   LIBER   ✦

Rabe Rest in Peace: Confirmation of the Rabe–Kindler Conversion of d-Quinotoxine Into Quinine: Experimental Affirmation of the Woodward–Doering Formal Total Synthesis of Quinine

✍ Scribed by Aaron C. Smith; Robert M. Williams


Publisher
John Wiley and Sons
Year
2008
Tongue
English
Weight
429 KB
Volume
120
Category
Article
ISSN
0044-8249

No coin nor oath required. For personal study only.

✦ Synopsis


Society both entitled "The Total Synthesis of Quinine". [1] This now famous full paper has been the subject of much attention over the years, particularly recently. It is now well-understood, that the Woodward-Doering "total synthesis" was actually a "formal" total synthesis of quinine (1) that relied on a seminal 1918 publication by Paul Rabe and Karl Kindler, wherein d-quinotoxine (2), the final synthetic substance in the Woodward-Doering work, was converted into quinine by a three-step sequence (Scheme 1). [2] This sequence involved: 1) oxidation of d-quinotoxine with sodium hypobromite to produce "N-bromoquinotoxine" (3); 2) base-mediated cyclization of 3 to produce "quininone" (4); and 3) aluminumpowder reduction of "quininone" to produce quinine (1) and quinidine (6, as a minor product). The 1918 paper, termed a "preliminary notice" by the authors, provided only a terse summary of this three-step process. This paper referenced Rabes 1911 conversion of cinchotoxine into cinchoninone and cinchonidinone (employing the analogous reactions for the quinotoxine to quininone and quinidinone conversion) [3] but subsequently in 1932, complete experimental details for the reduction protocol were published. [4] Despite the significant fanfare accompanying the publication of the Woodward-Doering paper during World War II, and the ensuing rich history of quinine and the Cinchona alkaloids in modern medicine, [5] it is surprising that apparently no one has reported efforts to simply attempt to repeat the Rabe-Kindler conversion of d-quinotoxine into quinine. This is particularly significant since concomitant with their relatively recent total synthesis of quinine, [6] Gilbert Stork and co-workers raised some possible doubts about the validity of this conversion, referring to Woodward and Doerings "total synthesis" as a "widely believed myth." [7] Consequently, the Woodward-Doering claim for a "total synthesis" albeit as a "formal" total synthesis by relay through d-quinotoxine based on the Rabe-Kindler sequence, has been besmirched. [7] This fascinating saga, spanning more than eighty years, was meticulously researched very recently by Seeman whose 2007 publication entitled: "The Woodward-Doering/Rabe-Kindler Total Synthesis of Quinine: Setting the Record Straight", [8] helped kindle our own interest in this story. In his analysis of all the available data in the literature and in archival materials, Dr. Seeman stated: "I conclude that Paul Rabe and Karl Kindler did convert d-quinotoxine into quinine Scheme 1. Conversion of d-quinotoxine (2) to quinine (1). a) NaOBr, NaOH, HCl (aq), Et 2 O, 55 % yield of crude product; b) NaOEt, EtOH, 88 % yield of crude product; c) aluminum powder, NaOEt, EtOH, 5 % yield (as the tartrate salt).


📜 SIMILAR VOLUMES