Phyto Chemistry

The chemistry of the essential oil of davana has been more extensively studied than any other aspect of this plant. Further, most of these studies have been carried out only after 1970 and not in India, where davana oil is exclusively produced, but in other countries. The reasons for these facts are not difficult to guess. Although the cultivation of davana is restricted to a small geographical area in south India, studies on the chemistry of its essential oil are not restricted by any such agro-climatic requirements and hence could be carried out anywhere. The availability of commercial quantities of davana oil only after 1970 (Sugunakar, 1987), and relatively easy accessibility to modern analytical instrumental facilities for evaluating the quality of essential oils in developed countries, may also be a reason for more studies on this oil having been carried out after 1970 and outside India; further, the oil is hardly used in India.

Apart from being the most extensively studied aspect, the chemistry of the essential oil of davana has also been periodically reviewed (Lawrence, 1978, 1988, 1995; Verghese and Jacob, 1984; Akhila and Tiwari, 1986; Mallavarapu, 1995). Studies on davana oil prior to 1967 were mainly restricted to its physico-chemical properties (Table 2).

The first work on the chemistry of davana oil was done by Sipma and Van der Wal (1968), who isolated davanone, the major constituent of the oil. This was later shown to be cis-davanone and is odourless (Thomas and Pitton, 1971; Thomas and Dubini, 1974). Several compounds, including linalool, linalool oxides, lilac aldehydes, lilac alcohols, cinnamic acid, geraniol, nerol etc., as well as sesquiterpenes, oxygenated sesquiterpenes and dihydrofurano sesquiterpenoids have been identified from davana oil. These are compiled, mainly from review articles cited above and presented in Table 3, in chronological order. Significant findings among these appear to be identification, isolation and structure determination of compounds responsible for the characteristic odour of davana oil viz., davana ether (Thomas and Pitton, 1971), davanafurans (Thomas and Dubini, 1974a), dihydrofurans (Chandra et al., 1987), a- and jS-dihydrorosefurans, trans-hydroxy davanone, hydroxy

Table 2 Physico-chemical properties of davana (Artemisia pattens) oil.

Reference Colour Odour Specific Refractive Optical gravity index rotation

Rao et al.

Dark

Pleasant

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