Synthesen in der Biotinreihe. III. DL‐epi‐Biotin, DL‐epi‐allo‐Biotin und zur Konfiguration der Biotinisomeren

Abstract

The results of our measurements are evaluated to support the \-a\lidity of more modern theories. Out of the relation between molecular weight and sedimentation constants the length of the preferential dement A m and the hydrodynamical thickness of the chain tl, are ealculated according t o the work of Kuhn & Edm. The results are found to be 8,s em for Am and 4 a lop8 cm for d,. The viscositymolecular weight relation is graphically evaluated in the usual double logarithmic form, which runs : *Imong the theoretical statements for the calculations of this relationship the one of Debye$ Bueche agrees most closely with our experimental results.An expression for the molar frictional ratio f/fo is tierived for the special case of total immobilisation of the solvent. For this ratio proportionality to the sixth root is found according to the theories mentioned. I n view of this we point to the fact that comparatively high f/f,-values can be well explained on the strength of the modern theories anti have not to be interpreted simply as asymmetric factors. [r)] 3 , O . lop3 . M'JgS. Wissenschaftliche Laboratorien der P. Hoffmann-La Roche & Co. Aktimgeselkchaft, Basel. 114. Synthesen in der Biotinreihe. 111. DL-epi-Biotin, m-epiallo-Biotin und zur Konfiguration der Biotinisomerenl) von C. A. Grob und H. von Sprecher. (14. 111. 52.)Wir heschreiben im Folgenden die Sjynthese zweier Isomeren cles Kiotins (I), niimlich des nL-epi-Biotins und des D~-epi-allo-Biotins. niese vor mehreren Jahren durchgefuhrten Arbeiten laufen auf die Synthese zweier isomerer 2-( o-Carboxybutyl)-3,4-diamino-thiophane (IXb) hinaus. Die vier m8glichen R'acemate dieser Struktur, deren wahrscheinliche Konfigurationen weiter unten diskutiert werden, sind wither in der Literatur beschrieben worden2).Die vorliegenden Synthesen, deren Stufen durchu-egs mit befriedigenden Ausbeuten verliefen, gehen von cf~-Carhomethoxyvaleral-

Biotin: A Timeless Challenge for Total Synthesis

“…The early approach of Grob and von Sprecher (1952) is rather straightforward in concept but did not lead to the correct biotin stereoisomer (Scheme ) . Central in the approach stands the conjugate addition of ammonia to the unsaturated nitro derivative 224 .…”