Viridifloric acid

The acid components required for the synthesis of the ester alkaloids, (+)-trachelanthic and viridifloric acids, were synthesised by stereospecific routes, since the relative stereochemistry of the asymmetric centres in these acids was still uncertain. Eventually they were obtained by appropriate stereospecific icis or trans) hydroxylation of trans-2-isopropylcrotonic acid (34), and its cis-isomer obtained by photochemical isomerisation. After resolution, (+)-trachelanthic acid was identified as the t/irco-2-isopropyl-2,3-dihydroxybutyric acid (35) the corresponding erythro-isomet was identified as viridifloric acid. 

The enolate of a,P-diaIkoxy ester (105) reacts with acetone to give (106) in good yield (equation 80) the product has been converted into (+)-viridifloric acid. ° ... 

The relative configurations at the asymmetric carbons were decided through the stereospecific synthesis of ( )-viridifloric acid, again on the assumption of CLXVIl as the structure of the precursor a-isopro-pylcrotonic acid. Traws-dihydroxylation of a-isopropylcrotonic acid was effected by Dry and Warren (184) by conversion with perbenzoic acid to the epoxide (not isolated), which was hydrolyzed with aqueous sulfuric acid to ( )-er2/phenacyl ester, m.p. 123-124°) by pertungstic acid oxidation of a-isopropylcrotonic acid. The... 

CLXXI), but whether hydroxylated trachelanthic or viridifloric acid has not been decided. Men shikov and Petrova (110) established the structure (of macrotomic acid) by periodate cleavage of macrotomine. A mole of oxygen was consumed per mole of alkaloid, and acetone, oxalic acid, and acetaldehyde were detected. The same products were... 

A new procedure of resolution of trachelanthic acid has been demonstrated by Kulakov et al. (144) by using the salt (mp 156°-158° [a]o — 9.4°) of (+ )-trachelanthic acid and (— )-benzylmethylamine. The previous structures advanced for trachelanthic and viridifloric acids have been confirmed by Likhosherstov et al. (145). 

Cjmaustine, C15H27NO4, a pale yellow gum ([aJi, +13.2° picrate, mp 135°-I36°), hydrolyzed to (— )-viridifloric acid and (+ )-supinidine. This is the first isolation of an ester of a (+ )-enantiomer of an allylic "necine base. 

C. av strale gave two new pyrrolizidene alkaloids cynaustraline, C15H27O4N (amorph. picrolonate, mp 149°) and cynaustine, C15H25O4N (amorph. picrate, mp 135°). Hydrolysis of these bases gave viridifloric acid in both cases and (-f )-isoretronecanol and (-f- )-supinidine, respectively. 

Three new alkaloids [(35)-(37)J were present in this mixture, together with symphytine (38). The structure (35) for 7-acetyl-scorpioidine was established by spectroscopic data, by hydrogen-olysis of (35) to give 7-acetylretronecanol, and by alkaline hydrolysis of (35) to yield retronecine (1), acetic, tiglic, and (2S,3S)-viridifloric acids. Scorpioidine (35) was also separated and gave (35) on acetylation. An epimer of scorpioidine, anadoline (39), was previously isolated from two Symphytum species (cf. 

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