Levopimaric acid

Fig. 3. Resin acids in rosin sizes, R = CH(CH2)2- The rosin acids are represented here as abietic acid [514-10-3] (1) and levopimaric acid [79-54-9] (2). In rosin there are other isomers and disproportionation products. The product of reaction with fumaric acid (3) is levopimaric acid— fumaric acid adduct...

The structures and nomenclature for the common pine resin acids based on the abietane skeleton (abietic-type acids) are given in Fig. 8. The abietic, neoabietic, palustric and levopimaric acids differ only in tbe location of tbeir two double bonds. All double bonds are endocyclic, except in the neoabietic acid in which one is exocyclic. 

Isolation, levopimaric acid from pine resin, 45, 64... 

In recent years ADC compounds have found wide use in the protection of 1,3-dienes. The Diels- Alder adducts, which because of the powerful dienophi-lic properties of ADC compounds are formed under mild conditions, can be reconverted to the diene by a series of hydrolysis, decarboxylation and oxidation reactions, followed by spontaneous loss of N2 (Scheme 18). In the preparation of cyclic azoalkanes (Section IV,D,2) a hydrogenation step is usually included (Eq. 19). The sequence is exemplified in Paquette s use of PTAD to protect the diene system of [4.4.2]propella-2,4,ll-triene,216 and in the protection of the diene system in levopimaric acid.217 However, in the... 

If the rotation is —210° or more negative, the next re-crystallization may be omitted and the levopimaric acid generated directly. 

The maximum observed rotation for the 2-amino-2-methyl-1-propanol salt of levopimaric acid is [a] n —218°. Methanol and ethanol solutions give the same specific rotations, but methanol is the preferred solvent because the time required to effect solution in ethanol is longer. If pure levopimaric acid, m.p. 151-153°, [a] D —276° is desired, the salt with —210° rotation should be dissolved in 8 parts of boiling methanol, the solution concentrated to the point of incipient crystallization, cooled, and filtered. The yield in this recrystallization is about 70%. 

After an induction period of approximately 1 week, the amine salt begins to be oxidized by air and the salt should be converted to levopimaric acid as soon as possible after it has been isolated. 

The yields obtained using this procedure can vary with the source of the oleoresin the submitters report a yield of 29-34% of levopimaric acid. 

Amino-2-methyl-l-piopanol in isolation of levopimaric acid, 45, 64 Amino-2-propanone, semicarbazone HYDROCHLORIDE, 46,1 Ammonium chlorophenyldithiocarba-mate, 46, 21... 

In a 1-1. separatory funnel there are first placed 400 ml. of ether and 75 ml. of 10% phosphoric acid (Note 10), and then the above amine salt is added (Note 11). The mixture is shaken vigorously for a few minutes, an additional 50 ml. of 10% phosphoric acid added, and the vigorous shaking continued until a ll the solid has disappeared. The ether layer is separated, washed twice with 100-ml. portions of water, and dried over anhydrous sodium sulfate. The drying agent is separated by filtration, the ether is removed at room temperature under reduced pressure using a rotary evaporator, and the residue dissolved in 40-60 ml. of boiling ethanol. The levopimaric acid is collected by suction filtration, yield 26-31 g. (10-12%), m.p. 147-150°, —265°... 

The described process of isolating levopimaric acid is based on the method of Summers, Lloyd, and Hedrick. The procedure, a modification of the process devised by Harris and Sanderson and Loeblich, Baldwin, O Connor, and Lawrence, is more convenient and gives improved yields. 

Two endoperoxides, 351 and 352, were obtained from optically active a-phellandrene (550),242,243 indicating that no steric hindrance is exerted by the isopropyl group of 350 on an oxygen attack. Stereoselective oxygenation is observed with ergosterol (555),19,22,23 lumisteryl acetate (555),244 levopimaric acid (557),245,246 and the benzoic ester of 6/3-hydroxy-5,5,9-trimethylhexahydronaphthalene (360),247 to mention... 

Fig. 5-5. Examples of resin acids. 1, Pimaric acid 2, sandaracopimaric acid 3, isopimaric acid 4, abietic acid 5, levopimaric acid 6, palustric acid 7, neoabietic acid 8, dehydroabietic acid.

The low-temperature ozonolysis of podocarpa-8,1 l,13-trien-12-ol (59) to form the lactol (60) has been re-examined54 and the importance of slightly acidic reaction conditions has been noted. The conversion of podocarpic acid into 19-hydroxypodocarpa-8(14)-en-13-one has been described.55 The C-12 oxygen function was removed by hydrogenolysis of the 12-toluene-p-sulphonate. Details of the nitration of methyl 7-oxodehydroabietate have appeared.56 The conformational analysis of the ring C diene, levopimaric acid, has been discussed57 in terms of a folded conformation. 

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