sponding t o 0.05 and 0.60 RF unit using Equation 7 . The range of RF values (0.05 to 0.60) 15 as chosen because greater resolution is generally achieved in this range than a t higher RF values. where diffusion and zone spreading become pronounced. Figure 1 shons the results in bar graph form and shons that nithin these ranges there is considerable overlap among the various solvent systems. Thus a quantitativr interrelation of seven chromatographic solvent systems has been obtained which can be used to cover the [Ru] range continuously from t 2 . 5 4 to -2.34 units. K h e n the calculated [ R u ]valuc, of a compound lies nithin the ranges of tmo solvent systems. it has generally been profitable t o use the less polar system for optimum resolution. The application of Equation 7 implies that the ilR,w values of individual substituents in the extrapolated solvent systems are directlj proportional to the ARII values of the substituents in the reference toluene-propylene glycol system. This direct relationship of ARlf values in the various solvent systems illustrates hy reversals in order of polarity are usually not observed upon changing solvent systems, thus eliminating the possibility of twodimensional paper chromatography for steroids. T o extend these relationships to the androstane series, a n assumption was made that the 17-keto and 178-hydroxy1 groups had 4R.,f values approximately equal t o their polar counterparts in the pregnane series, and accordingly 4Rtf values of 0.76 and 1.56 were assigned t o the 17-keto and 178hydroxyl, respectively. Using these
values, a calibration curve similar to that used to derive a value for the pregnane nucleus (-3.00) yielded a 4R.v value of -2.45 for the androstane nucleus. This higher (less negative) value for the androstane nucleus explains the greater polarity of androstane derivatives as compared to similar pregnane derivatives. Use of these values has resulted in satisfactory agreement betneen calculated and e\perimental mobilities in thcse solvent systems, but with somen hat higher average deviations. T o evaluate the usefulness of the systematic approach to steroid paper chromatography, chemically related series of compounds (10) were used instead of fortuitously chosen unrelated steroids. The compounds listed in Table IV comprise steroids involved in the laboratory synthesis of dexamethasone. The accuracy of the method in predicting desired solvent systems and approximate chromatographic mobilities can be judged by examining the data listed in Table IT'. Although the agreement betneen the calculated and experimental [ R Y ]values is not as good as one would like, nevertheless it is fair enough t o permit the choosing of the proper paper chromatographic solvent system, as evidenced by a comparison of the calculated and experimental RF values. The worst deviation encountered corresponds t o an error of only 0.64 [R,tf]or 0.33 Rp unit in the corresponding solvent system, while the average RF deviation is only 0.09 RF unit. This systematic approach to steroid paper chromatography makes possible the prediction of the approximate
mobility of a steroid of the pregnane and androstane series in all of the seven solvent' systems by inspection of its struct,ure and has thus greatly simplified routine paper chromatographic analyses. It is capable of extension to other steroid families and other solvent systems and makes steroid paper chromatography a little lrss of a n art. LITERATURE CITED
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(8) lfartin, .A. J. P., Biochein. SOC.Symposia 3 , 6 (1950). ( 9 ) Seher, R., J . Chromatog. 1, 205 (1958). 110) Oliveto. E. P.. Rausser. R.. Weber. L.. Nussbaum. L.. kebbrt. W.1 Coniglio, C. T., H&hberg, E. B.: Tolksdorf, S., Eider, hI., Perlman, P. L., Pechet, 11. hI. J . Am. Chem. Sac. 80, 4431 (1958) i l l i Reineke. L. AI., AAsa~. C H m r . 28. 1853 (1956) (12) Savard, I
