Theophylline is related chemically to the natural metabolite xanthine.
A third explanation of xanthine action is that these agents cause the production and release of endogenous catecholamines, which in turn could cause muscle tremor, tachycardia, and bronchial relaxation.
Xanthine is a chemical structure consisting of two adjacent rings--one containing two nitrogen atoms and four carbon atoms, and the other containing two nitrogen and three carbons.
Eventually their structure formula was determined and they were also found to be derivatives of Xanthine, but with only two methyl groups in different positions on the side chains; one was named Theobromine and the other Theophylline.
The compound of choice was to have one of the-methyl groups replaced by a longer side chain containing an oxygen atom with the rest of the molecule being a di-methyl Xanthine.
In this day and age, emphasizing its identity as a Xanthine derivative would be practically a kiss of death with all anticaffeine propaganda prevalent.