Reactions of the Ansamycins

Due to the symmetry of the dimethyltetrahydroxynaphthoquinone there are only two positions for the acyl group of dapmavarone - at C-5 or C-6. The pmr spectrum of dapmavarone shows that its acyl chain actually contains a cyclic ether, with an ether oxygen substituted at the carbon 

An 8-hydroxy-1,4-naphthoquinone nucleus was established in (a) by spectroscopic properties and pKa of streptovarone, while the pyruvamide 

Surprisingly little eifort has been expended in attempts to prepare derivatives of streptovaricins with improved chemotherapeutic properties, compared to the enormous (and successful) effort directed toward rifa- 

Most spectral properties (uv, ir, pmr, mass spectral) are nearly identical for the isomers. The natural isomers show intense positive rotations at the D line of sodium, while the atropisomers show equally intense negative rotations (streptovaricin C, [a] - -602° atropisostreptovaricin C, [a] — 551°), and the circular dichroism curves of the atropisomers are nearly mirror images, as shown in Fig. 10. Surprisingly, the biological properties 

Derivatives of streptovaricins also can be converted to their atropisomers, sometimes at lower temperatures than the streptovaricins themselves. In refluxing benzene an equilibrium mixture of streptovaricin C triacetate and its atropisomer is formed. This reaction led to a complication in assigning the structure of streptovaricin C by x-ray crystallography (149), since the x-ray study was carried out on a cyclic / -bromobenzene-boronate formed by heating streptovaricin C triacetate in benzene with /7-bromobenzeneboronic acid and the atropisomeric cyclic /7-bromo- 

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