Pharmacognostical and biological studies of Kenyan Lippia species with special reference to their essential oil content

Abstract

The study of essential oils of all 8 Lippia species (Verbenaceae) naturally occuring in Kenya Lias carried out. The essential oils were obtained by hydrodistillation and analysis was mainly carried out by GLC and GC/MS. Two cheroical varieties (chvar) of Lippia ukambensis mere found on the basis of their camphor and 1,8-cineole content. These were thus designated Lippia ukambensis chvar camphor and Lippia ukambensis chvar cineole. The essential oil yield from _L. ukambensis chvar camphor averaged 1.8% while it was 1.6% from JL. ukambensis chvar cineole. J_. ukambensis chvar camphor oil contained an average of 37.3% camphor with only traces of 1,8-cineole. L. ukambensis chvar cineole on the other hand had an average of 23.7% 1,8-cineole while camphor accounted for an average of only 1.1%. The other difference in chemical composition of these varieties was the presence of borneol in _L. ukambensis chvar camphor oil and its absence in _L. ukambensis chvar cineole oil in which c<-terpineol was present instead. Other significantly different compounds between the chemovarieties were camphene, limonene, p-cymene which were more in L. ukambensis chvar camphor oil and, 3-carene, trans-sabinene hydrate, ,6-cubenene and terpinert- L-ol which were more in L. ukambensis chvar cineole oil. (xxiii) Trans-sabinene hydrate was one of the major compounds in both chemovarieties with an average of 18.9% in the essential oil of ukambensis chvar camphor and 2U .7% in that of J_. ukambensis chvar cineole. The major compound in Lippia somalensis oil (0.7%) mas 1,8-cineole (average 31.9%). This essential oil had a lot of qualitative chemical similarities and quantitative differences with those from L. ukambensis chemical varieties. These differences and similarities were compared by using 15 compounds found in the oils of these Lippia species. It mas found for example, that uhile no camphor, trans-sabinene hydrate and borneol mere detected in J_. somalensis oil, this oil had more 3-carene, p-cymene, myrcene, limonene, ^-ocimene and y-terpinene than both essential oils of j_. ukambensis chemical varieties. Many other quantitative differences were noted. The essential oil of Lippia dauensis (2.L%) contained ocimene (2L.7%), 2-methyl-6-methylene-7-octen-L-one (15.7%) myrcene (12.9%), cis-taqetone (11.0%) and 2-methyl-6- methylene-2, 7-octadien-L-ol (9.L%) as the major components The other significant compounds in this oil were £-cymene, dihydrotagetone, trans-taqetone and <x?-terpinene. The essential oil of Lippia .javanica (average 1.6%) contained myrcenone (average 32.9%), cis-ocimenone (average 31.9%), trans-ocimenone (average 15.8%) and myrcene (average 7.5%). Cis-ocimenone changed into a very polar reddish-brown compound unless the oil was stored in the deep freezer (xxiv) 0-Carvone (average 60.0%) was the major compound in the essential oil of Lippia carviodora (average 3.0%). Limonene and carvinyl acetate were the other major compounds in this oil. Lippia carviodora var minor oil (0.2%) on the other hand contained mainly sesquiterpene hydrocarbons with jS-cubenene (32.0%) and jB-elemene (13.7%) being the major components. It was therefore clear that the composition of essential oil of L. carviodora and L. carviodora var minor were very different. A substantial amount of salicylic acid was isolated from the diethylether fraction of methanol soxhlet extraction of L. carviodora var minor leaves. Limonene (average 36.2%), piperitone (average 27.2%) and piperitenone (average 9.L%) were the major compounds in the essential oil of _L. wilmsii (1.1-2.2%). Other notable compounds in this oil were linalool, 1,0-cineole and 'B'-terpinene. The essential oil of Lippia qrandifalia (0.7%) contained linalool (L6.1%), thymol (15.2%), /-cubenene (11.7%)and £-cymene (10.L%) as the major components. The antimicrobial tests of the essential oils showed that j.. grandifolia oil and _L. javanica oil were the most active. Indeed, _L. grandifolia oil was fungicidal to Colletotrichum coffeanum at a minimum inhibitory concentration (MIC) of 50 /jg/ml. This is the causitive agent (xxv) of Coffee Berry Disease which is one of the most prevalent and feared diseases in coffee farming in Kenya. The oil was also fungicidal to Microsporum auctauinji at its MIC ICO >jg/ml, _M_. canis and Candida albicans at 500 jjg/ml. The antibacterial activity of _L. qrandifolia oil on a number of common bacteria was also carried out. This essential oil was active against Staphylococcus aureus, _S. albus, Bacillus cereus and Escherichia coli at MIC 500 jjg/ml. The other essential oil with notable antimicrobial activity was fresh Lippia javanica oil which exhibited MIC 500 ,ug/ml for Candida albicans and Colletotrichum coffeanum and 1000 jjg/ml for most of the other microorganisms tested. The essential oils of J_. dauensis and L. javanica were the most active oils as larvicidal agents, having LD50 of 660. ppm and 7U.1 ppm respectively. The larvicidal activity of some of the oxygenated and hydrocarbon monoterpene ingredients of essential oils of Lippia species is also reported. Generally, hydrocarbon monoterpenes were the most active. The bioassay of the repellant activity of essential oils of Lippia species to maize weevils (Sitophilus leamais) showed that most of the oils were more active than the synthetic standard, DEET (N,l\l-diethyltoiuamide) at (xxvi) various dose levels. L. ukambensis chvar cineole had the lowest activity in comparison with the other oils of Lippia species or the standard. The essential oil of L. ukambensis chvar camphor was the most active at the lowest dose level tested (0.625 jjI) being 1.5 times more active than DEET. All the essential oils of Lippia species had a marked spasmolytic effect on the isolated ileum and trachea. The oils also reduced the force of contraction of the heart. In view of the ease of cultivation of these plants, agreeable aroma of their oils due to the favourable constituents and the biological activities of the essential oils of Lippia species in Kenya, it is suggested that these plants are suitable for possible commercial exploitation