1249 of Va with BOC-Ser-NHS and crystallization of the product of VIIIa (0.233 g, 0.25 mmole) in EtOH (45 ml) was hydrogenated (VI), afforded BOC-Ser(BZL)-Gly-Gly-Pro-Leu-Val-OCH3~Hz0 over 10% palladium~harcoal(O.11g) at 23" for 5.5 hr, consuming 1.4 g, 81 t11p 85-90", Rr (S-I) 0.75, Ri (S-VI) 0.32, [(Y]"D -70.7' an equivalent volume of Hz. The suspension was filtered through (c 0.308, methanol). Anal. Calcd for C36He6010Ne~0.5Hz0Celite, the filtrate was evaporated, and the residue was dried over (recrystallized sample, mp 85-88"): C, 58.58; H, 7.78; N, PzOa. The product, HCl~H-Gly-Asp-Ser-Gly-G1y-Pro-Leu-Val11.19; H 2 0 , 1.2. Found: C, 58.32; H, 7.83; N, 11.31. A OCHa(IX), 0.18 g, 96% yield, mp 151-156", R f(S-I) 0.11, was de1.1 weight loss was found upon drying to constant weight at 80" void of ultraviolet benzylic absorption at 257 mp. Crystallization (0.2 mm). from EtOH-EtOAc led to granular crystals, mp 158-160", [ ( Y ] ~ ~ D D. BOC-Gly-Asp(OB2L)-Ser(B2L)-Gly-Gly-Pro-Leu-Val- -106" (c 0.057, HzO). Anal. Calcd for C30H5101zN18Cll~ OCH3 (VIII). The BOC protecting group was removed from VI, CzHjOH: C, 48.20; H, 7.21; N, 14.05; CI, 4.45. Found: C, affording HCI .H-Ser(BZL)-Gly-Gly-Pro-Leu-Val-OCH3 (VIa), 48.35; H,6.98; N, 13.94; CI,4.48. 100 R r (S-I) 0.45. VIa was coupled with BOC-Asp(0BZL)-NHS Compound IX (2.25 mg) was digested with a mixture of preinin the usual way, except for omission of alkali washing during the cubated solutions of 0.1 leucine aminopeptidase and prolidaseZ4 work-up procedure (in view of the known" base-catalyzed rear(0.5 ml of each, 1 mg/ml of MnCL.4Hz0, 0.025 M Tris buffer, rangement of Asp-Ser sequences), yielding BOC-Asp(0BZL)-SerpH 8.5, 37", 69 hr). Thin layer chromatography (silica gel H ; (BZL)-Gly-Gly-Pro-Leu-Val-OCH3 (VII), 98 %, R r (S-I) 0.80, R r (Sn-BuOH-HOAc-H20, 2 :1 : 1, in milliliters ; CsH50H-Hz0, 3 :1, in VI) 0.56. A solution of VI1 (1.58 g, 1.69 mmoles) in DME (4.0 ml) grams) of the digest accounted for all constituent amino acids and was treated with 6.1 N HCI-DME (1.24 ml, 7.6 mmoles) at 0" for 4 did not detect peptides with chlorine-tolidine, Samples of enzymic hr and worked up as previously indicated, leading to HCI .H-Aspand acid (6 N HCI, 110", 24 hr) digests were analyzed with the (0BZL)-Ser(BZL)-Gly-Gly-Pro-Leu-Val-OCHg (VIIa), 1.47 g, Beckman-Spinco analyzer. The amino acid ratios are given in 99% yield, R r (S-I) 0.50. VIIa was coupled with BOC-Gly-NHS Table I. as above, and the product, BOC-Gly-Asp(0BZL)-Ser(BZL)Acknowledgment. We thank Dr. George W. AnderGly-Gly-Pro-Leu-Val-OCH3 (VIII) crystallized from hexaneethanol, 1.20 g, 777& mp 122-130", Rr (S-I) 0.74, Rr (S-VI) 0.16, son for helpful discussions, Dr. Susan Dowd for val[@D -62.5" (c 0.320, methanol). Anal. Calcd for C4QH70uable assistance in the preparation of several interOlaNa (recrystallized sample, mp 130-133': C, 59.14; H, 7.09; mediates, and Dr. Elizabeth Simons for help and advice N, 11.26. Found: C, 58.90; H,7.06; N, 10.99. in the enzyme hydrolysis studies. Amino acid analyses E. HCI H-Gly-Asp-Ser-Gly-Gly-Pro-Leu-Val-OCHa (IX). Rewere carried out by Miss Mary Jane Becherer. moval of the BOC group from VI11 was carried out as described in part D, leading to HCI 'H-Gly-Asp(0BZL)-Ser(BZL)-Gly-Gly(24) See footnote b, Table I. Pro-Leu-Val-OCHa (VIIIa) in 98 yield, Rr (S-I) 0.41. A solution
x,
z,
.
The Crystal and Molecular Structure of 2,4-Dithiouraci11 Eli Shefter and Henry G. Mautner Contribution f r o m the Department of Pharmaceutics, School of Pharmacy, State Uniuersity of New York at Buffalo, Buflalo, New York, and the Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut. Received October 20, 1966 Abstract: The molecular structure of 2,4-dithiouracil has been determined by X-ray diffraction. The crystals are monoclinic, space group P2,/c, a = 4.247 A, b = 14.586 A, c = 9.907 A, 0 = 98.77", a n d 2 = 4. Evidence is presented that dithiouracil contains highly polarized thionamide groups, the polarization of these groups being position dependent. The C-S bond lengths were found to be 1.645 and 1.685 (10.006) A. The packing of the molecules in the crystal lattice is dominated by S . . . (H)-N hydrogen bonds. The lengths of the hydrogen bonds appear to be a function of the degree of polarization about the sulfur atoms.
N
umerous sulfur-substituted pyrimidines and purines have found applications as clinically useful drugs. In many of these it was noted that the position in which sulfur was introduced was crucial to biological activity. For instance, 2-thiouracil, but not 4-thiouracil, has useful antithyroid activity, while 6-thioguanine and 6-mercaptopurine, but not the corresponding 2-thio compounds, exert antineoplastic a ~ t i o n . ~4-Thiopteridines and -pyrimidines and 6-thiopurines, but not the (1) This work was supported, in part, by grants from the National Cancer Institute and the National Institute of the U. S. Public Health Service (CA-3937-08 and 4-F2-GM-22, 830-02) and the National Science Foundation (GB-4114). We are also very much indebted to Professor David Harker for extending us the use of the Crystallographic Center of Roswell Park Memorial Institute, and to the Computing Center of the State University of New York at Buffalo for a generous gift of computer time. (2) E. B. Astwood, A. Bissell, and A. M. Hughes, Endocrinology, 37, 456 (1945). (3) R. I
