CH / | \ / | \ H_{2}C CH_{2} CH--CH==CH_{2} | | | H_{2}C HO·C CH_{2} \ / | / \/ | / /\ | / / \ | / CH_{2} N / HC C // \ C / \\ CH_{3}OC| \ / |CH HC| | | |CH \\ C \ // HC N the formula being C_{20}H_{24}N_{2}O_{2}. Quinine has not been completely synthesised, but it has been prepared from cupreine, another cinchona alkaloid. The strychnos alkaloids likewise have not yet been artificially prepared, and their structure still requires elucidation. The derivatives of isoquinoline, which was discovered by Hoogewerff and van Dorp in 1885, include some of the opium alkaloids, papaverine and narcotine, for example. Morphine and codeine do not, strictly speaking, fall into either of the three groups mentioned; our knowledge of the chemical nature of these substances has been much advanced recently, and it is probable that their synthesis will be effected before long. HC CH // \ C / \\ HC| \ / |CH HC| | | |N \\/ C \ // HC CH Isoquinoline. One of the most beautiful pieces of work on the synthesis of vital products during recent years was the artificial preparation by Fischer (1895–98) of the bases caffeine and theobromine. The processes employed are too long and complicated to be described here, but the formulas may be given, since they demonstrate the close relationship which exists between the two substances. (CH{3})N-----CO HN-----CO | | | | | | | | CO C-N(CH{3}) CO C-N(CH{3}) | || \ | || \ | || /CH | || /CH (CH{3})N-----C-N (CH{3})N-----C-N Caffeine. Theobromine. OTHER SYNTHETIC PRODUCTS. (_Benzoic acid, camphor, adrenaline, salicylic acid._)