SUMMARY 3The H NMR spectra of a series of 7 steroids tritiated at C ( l ) , C ( 2 ) , C ( 6 ) , C ( 7 ) , C ( 9 ) and C ( 1 6 ) yield quantitative information on the 3H distribution i n these compounds. Deuterated chloroform i s not a good solvent to examine the regio-and stereospecificity of the labelling process for acid labile positions such as C(2) in a 3-oxosteroid and C ( 6 ) in a 8-0x0-0 -steroid. 4

The synthesis, purification and analysis of three tritiated neuropeptides are described. Org 2766 (an ACTH (4-9) analogue) and Org G K 78 (des-Tyr-y-endorphin) were labelled in the aromatic ring of phenylalanine by catalytic deiodination of the (p-iodopheny1)alanine precursors using 3H,. Org 5878 (des-enkephalin-y-endorphin) was labelled in the lysine residue by reduction of the ~-2,6-diamino-4-hexynoic acid-containing analogue with 3H,. The peptides were purified by preparative HPLC using ammonium acetate buffer systems. The chemical purity was determined by ' H NMR, the radiochemical purity was measured by HPLC and the 3H distribution by 3H NMR. Specific activities (as determined by HPLC) were ca. 900 GBq.mmol-' for Org 2766 and Org G K 78 and 1400 GBq mmol-' for Org 5878. (1981).phosphate (pH 3)/methanol (65/35, v/v) or on LiChrosorb 10 NH, using a gradient of 0.01 M NH,OAc (pH 4.8) containing We are grateful to Dr. J. van Nispen and Drs. H. Greven for stimulating discussions and we wish to thank Mr. J. Thio for helpful technical assistance in the HPLC experiments.

Labelling of mianserin in the N-methyl group or the piperazine ring results in changes in the physical properties of the molecule. Using deuterium it is shown that mianserin can be labelled at metabolically stable positions wlthout introducing isotope effects by exchange under alkaline conditions (at Clo) or by reductive dechlorination (at C 3 -1 c13-HI-mianserin with a specific activity of 16 Ci.mmol was synthesized by reductive dehalogenation of 13-chloromianserin using 3H2. The position of the label was confirmed by 'H-NMR spectroscopy. or C13).

Abstract. Eleven deuterated analogues of mianserin have been synthesized and analyzed by 'H and I3C NMR. Based on these compounds, the aromatic part of the 'H spectrum of mianserin could be interpreted.

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