Synthesis of stereoisomeric mixture of compound newly proposed for "auxin b" by K. Buffel.

Abstract

In 1928, F. Went discovered the first plant hormone) and shortly after in 1933 F. Kogl and his co-workers isolated the compounds in crystalline forms and named them "auxins". In 1934, they reported the constitutions of auxins a (I) and b (II) .?),3) However, thereafter none has succeeded to re-isolate them by the same procedures from the same kinds of materials as were used by F. Kogl and his co-workers. The authors considered, if the proposed structures of auxins a and b are correct, the synthetic compounds having their structures must have biological activity as declared by F. Kogl et al. They took up auxin b as the synthetic target, because it has two less asymetric carbon atoms than auxin a. In 1966 the authors synthesized the stereoisomeric mixture of the o-lactone (III) of compound (II) proposed for auxin b by F. Kogl4> >~> and tested its activity on the premise that in extremely dilute aqueous solution, the lactone will afford auxin b itself by ring opening. However it did not show any biological activities as Kogl et al. declared.6) Shortly after, J. A. Vliegenthart and J. F. G. Vliegenthart reported7) that they re-investigated the samples of auxins a and b and relating compounds in the sample tubes left by Kogl in his laboratory and they found that the contents were totally different from the compounds reported by him and his co-workers. For example, the substance in the sample tube labeled "auxin a" was cholic acid, that labeled "auxin a lactone" was p-hydroquinone, that labeled "auxin b" was thiosemicarbazide etc. However, curiously the melting points of them are almost identical with those of the compounds in the reports of Kogl et al. Recently K. Buffel reexamined the reports relating to auxins by F. Kogl and his co-workers and other researchers. He newly proposed a structure (IV) as the most probable one for auxin b.8) The authors synthesized the compound (IV) and the isomeric compound (V) without any stereo-control. The first product theoretically contains the "natural auxin b" to the amount of one thirtysecond of it. However, to the authors' great regret, the both synthesized materials (IV) and (V) did not show any biological activities as F. Kogl stated. The biological tests were done by T. Nakamura and her co-workers and their details will be reported in separate papers.

Synthetic examination of incorrectly proposed structures of biomolecules

“…He thought the structure A for auxin‐a to be correct, but proposed a new structure F for auxin‐b 7. Three years later, Matsui synthesized F as a stereoisomeric mixture and found it to be biologically inactive 8. There is a possibility, however, that the non‐natural stereoisomer(s) in the synthetic E or F may inhibit the bioactivity of the natural isomer, just as in the case of the pheromone of the Japanese beetle 9…”