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This communication describes the application of the 2‐(methylsulfonyl)ethyl group (Mse) as a base‐labile protecting group for the two hydroxyl functions in phosphoric acid monoesters. Due to its perfect stability towards acids, the Mse group can function as a stable protecting group in a phosphochloridate, providing a suitable phosphorylating agent. Some model phosphorylations are presented, and the reaction is applied to the synthesis of bis[2‐(methylsulfonyl)ethyl] tyrosine phosphate. Removal of the Mse functions is achieved effectively and extremely rapidly in alkaline media. The estimation of the minimum conditions necessary for the removal of one or both Mse functions from bis[2‐(methylsulfonyl)ethyl] p‐nitrophenyl phosphate and from a tyrosine derivative is described.

Beta adrenoceptor function in central airway smooth muscle of patients with chronic airflow obstruction was investigated by radioligand binding studies and isoprenaline relaxation experiments. Receptor characteristics were determined in tracheal smooth muscle preparations obtained at necropsy from 12 patients and in bronchial tissue obtained at thoracotomy from 21 patients with chronic airflow obstruction. Receptor characteristics were compared with those obtained in airway tissue preparations from 65 control subjects without chronic airflow obstruction. The number ofbeta adrenoceptors, their binding affinity for the radioligand ['25I]-(-)-cyanopindolol, and the tissue binding characteristics of isoprenaline were similar in tissue from patients with chronic airflow obstruction and from control subjects. Isoprenaline induced relaxation of tracheal smooth muscle without precontraction by methacholine showed slightly (though not significantly) less sensitivity to isoprenaline in patients with chronic airflow obstruction than in control subjects (mean (SEM) pD2-the negative logarithm of the concentration producing 50% relaxation--632 (0'16) v 6-62 (0 15)). The same pattern of pD2 values was found in segmental bronchial strips without precontraction by methacholine (chronic airflow obstruction 655 (0'27), control 7 14 (0'12)). Isoprenaline relaxation in segmental bronchial strips when contracted maximally was significantly less in the patients with airflow obstruction than in the control subjects (pD2 value 5'99 (0-18) v 6'45 (0'07)). These results suggest that beta adrenoceptors in airway smooth muscle of patients with chronic airflow obstruction are not abnormal in number or in binding affinity but that there is less effective coupling between components of the relaxant system distal to the beta adrenoceptor. The possibility that the reduced isoprenaline sensitivity is a consequence of previous bronchodilator treatment cannot be excluded.