Perillic acid

By oxidation this alcohol yields perillic aldehyde which forms a semi-carbazone, melting at 199° to 200°, and perillic acid, melting at 130° to 131°. It also yields a naphthyl-urethane, melting at 146° to 147°. 

The oxime of perillic aldehyde melts at 102°, and when heated with acetic anhydride in presence of sodium acetate, is converted into the nitrile of perillic acid, a liquid having the following characters —... 

When perillic acid is dissolved in five times its weight of amyl alcohol and is reduced by sodium at the boiling temperature, dihydro-perillic acid, CjoH Oj, is obtained. This acid melts at 107° to 109° C. By the reduction of its methyl ester by means of sodium, dihydroperillic alcohol is fornned, which is a liquid with a rose odour and having the following characters —... 

Limonene was extensively metabolized by a variety of mammalian species [279, 290, 292, 301]. Its principal circulating metabolites identified in the rat were perillic acid and dihydroperillic acid. These components were effective inhibitors of isoprenylation and cellular proliferation in vitro [271]. 

Limonene and perillic acid remarkably reduced the lung metatastatic tumour nodule formation by 65 and 67%, respectively however, perillyl alcohol was considerably more potent than limonene against breast cancer [284, 302], rat mammary cancer and pancreatic tumours [288]. Phase 1 studies of d-limo-nene [303, 304] and phase I and phase II [305-311] studies of perillyl alcohol revealed dose-limiting toxicities nausea, vomiting, anorexia, unpleasant taste and eructation, and thus a maximum tolerated dose for perillyl alcohol was determined [305]. 

Limonene (92) is the most widely distributed terpene in nature after a-pinene [68]. The (+)-isomer is present in Citrus peel oils at a concentration of over 90% a low concentration of the (-)-isomer is found in oils from the Mentha species and conifers [26]. The first data on the microbial transformation of limonene date back to the sixties. A soil Pseudomonad was isolated by enrichment culture technique on limonene as the sole source of carbon [69]. This Pseudomonad was also capable of growing on a-pinene, / -pinene, 1-p-menthene and p-cymene. The optimal level of limonene for growth was 0.3-0.6% (v/v) although no toxicity was observed at 2% levels. Fermentation of limonene by this bacterium in a mineral-salts medium resulted in the formation of a large number of neutral and acidic products. Dihydrocarvone, carvone, carveol, 8-p-menthene-1,2-cw-diol, 8-p-menthen-1 -ol-2-one, 8-p-menthene-1,2-trans-diol and 1 -p-menthene-6,9-diol were among the neutral products isolated and identified. The acidic compounds isolated and identified were perillic acid, /Msopropenyl pimelic acid, 2-hydroxy-8-p-menthen-7-oic acid and... 

As mentioned before, a Pseudomonas incognita was isolated by enrichment technique on the monoterpene alcohol linalool that was also able to grow on geraniol, nerol and limonene [36]. The metabolism of limonene by this bacterium was also investigated [37]. After fermentation the medium yielded as main product a crystallic acid, perillic acid, together with unmetabolised limonene, and some oxygenated compounds dihydrocarvone, carvone, carveol, p-menth-8-en-1 -ol-2-one, p-menth-8-ene-1,2-diol or p-menth-1 -ene-6,9-diol (structure not fully elucidated) and finally / -isopropenyl pimelic acid. 

The same group has also isolated a strain of Pseudomonas putida-arvilla (PL-strain) from limonene and (+)-a-pinene as the sole carbon source that was capable of growing on (+)-limonene, (+)-a-pinene, (-)-a-pinene, / -pinene, 1-p-menthene, 3-p-menthene and p-cymene as substrates [75]. Limonene was degraded to perillyl alcohol, perillaldehyde and perillic acid. 

More recently the biotransformation of limonene by another Pseudomonad strain, P. gladioli was reported [76,77]. P. gladioli was isolated by an enrichment culture technique from pine bark and sap using a mineral salts broth with limonene as the sole source of carbon. Fermentations were performed during 4-10 days in shake flasks at 25°C using a pH 6.5 mineral salts medium and 1.0% (+)-limonene. Major conversion products were identified as (+)-a-terpineol and (+)-perillic acid. This was the first time that the microbial conversion of limonene to (+)-a-terpineol was reported, see pathway 4. The conversion of limonene to a-terpineol was achieved with an enzyme, a-terpineol dehydratase (a TD), by the same group [78]. The enzyme, purified more than tenfold after cell-disruption of Pseudomonas gladioli, stereospecifically converted (4 )-(+)-limonene to (4/ )-(+)-a-terpineol or (4S)-(+)-limonene to (4S)-(+)-a-terpineol. a-Terpineol is widely distributed in nature and is one of the most commonly used perfume chemicals [27]. 

Limonene inhibits the isoprenylation of a class of cellular proteins of 21-26 kDa, including p21ras and possibly other small GTP-binding proteins, in a dose-dependent manner in both cell lines (Crowell et al., 1991). Such inhibitors could alter signal transduction and result in altered gene expression (Gould, 1997). The two major rat serum metabolites of limonene, perillic acid and dihydroperillic acid, were more potent than limonene in the inhibition of isoprenylation (Crowell et al., 1991). These actions could explain the chemotherapeutic acitivity of limonene oils. 

Mo3l Perillic acid Metabolite of limonene NFkB. RAS 142,134,1371... 

Limonene is metabolized predominantly to (+)-perillic acid (103 R = CO2H) by Pseudomonas incognita, presumably via C-7 hydroxylation, which has also been reported in the conversion of a-terpineol into 7-hydroxy-a-terpineol in further work (see Vol. 8, p. 26) on callus cultures of Nicotiana tabacum and is also presumed to be involved to account for the isolation of oleuropeic acid (140)... 

---