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Examples of Total Synthesis 1262 COMMUNICATIONSTO THE EDITOR Tol. i9 methylation,s was converted into the trans product followed by crystallization from acetone-water IV, m.p. 202-204", C, 78.9; H, 8.33, in 69%.yield. containing an equivalent of pyridine, led to 75q) Alkaline peroxide oxidation4 transformed IV into V of D-a-phenoxymethylpenicilloicacid hydrate (IV), (R = H) which was converted with diazomethane CI~HZONZO~S.H~O;m.p. 129" dec. [Found: C, into the ester V (R = CHa), and cyclized with 49.61; H, 5.77; N, 6.94; aZ5D + 94" (c, 1 in potassium t-butoxide in benzene. The resulting methanol)]. Identity with a sample prepared by keto ester was decarbomethoxylated with hydro- saponification of natural penicillin V5 was estab- chloric and acetic acid to give the dl-ketone VI, lished by comparison of m.p., infrared spectra m.p. 155.5-161.5". The infrared spectrum of this (KBr), optical rotation and mixed m.p. material was indistinguishable from that of Treatment with N,N'-dicyclohexylcarbodiimide authentic 3,B-hydroxy-9,1l-dehydroandrostane-17- in dioxane-water (20 min. at 25') cyclized Was the one.g monopotassium salt in l(rl27, yield. By partition (S) At this stage the 3-hydroxyl group was protected as the tetra. between methyl isobutyl ketone and pH 5.5 phos- hydropyranyl ether (cf. ref. 3). phate buffer (two funnels) the totally synthetic (9) C. W. Shoppee, J. Ckem. SOC.,1134 (1946). crystalline potassium salt of penicillin V was iso- DEPARTMENTOF CHEMISTRY lated. The natural and synthetic potassium salts UNIVERSITYOF WISCOXSIN WILLIAMS. JOHNSON were shown to be identical by microbiological as- MADISON,WISCONSIN ALLEN,JR. DUFFS. say,6 optical rotation [synthetic, d5D -/- 223" RECEIVEDFEBRUARY 1, 1957 (c, 0.2 in water); natural, a25~+ 223" (c, 0.2 in water); reported,' Q?OD + 223" (c, 1 in water)], in- THE TOTAL SYNTHESIS OF PENICILLIN V frared spectra (KBr), m.p. 263" dec. (reported,' Sir: 256-260" uncorr.), undepressed upon admixture. The ability of aliphatic carbodiimides to form s amide bonds in aqueous solution directly from the /\ (1) C6HjOCH2COC1 amine and carboxyl components under very mild HCl'HzNCH-CH C(CH3)z (2) HC1 //I > conditions' suggested the use of these reagents for CO XH-CHCOZH (3) CsHsN the cyclization of a pencilloic acid to a penicillin. I We have Drepared by total synthesis in good over- OC(CHa)3 all yield the penicilloic acid corresponding to peni- 11, D-CY cillin V (phenoxymethylpenicillin). By use of N ,N'- S /\ dicyclohexylcarbodiimide cyclization was effected C6HsOCHzCOXHCH-CH C( CH3)z rapidly at room temperature, thereby completing //I the first rational synthesis of a natural penicillin.2 CO NII-CHCOzH Condensation of D-penicillamine with t-butyl I (1) KOH (one equiv.) OH f phthalimidomalonaldehydate afforded the t-butyl (2) CJ~lli\i'. C.=NCJTI, ~-a-4-carboxy-5,5-dimethyl-a-phthalimido-2- thi- I17 azolidineacetate (I), C2d&4N2O6S, m.p. 161" dec. S [Found: C, 57.45; H, 6.06; N, 6.83; aZ5~ /\ + 54" (c,l in acetic acid)] as described for the cor- CeHjOCHCONHCH-$If C(CII3)2 responding DL-a The a, or natural, CO-k--&HCO&I configuration of the more soluble (ethanol-water) penicillin V potassium I was established chemically by relationship to (potassium phenoxymethylpenicillinate) natural dimethyl D-cr-benzylpenicilloate. The less soluble D-y-iSOmer may be isomerized in high yield The same results were obtained using IV derived to the D-aform as in the DL-ester ~eries,~thus pro- from natural penicillin V. The entire series also has been carried through starting with DL-penicil- viding a stereochemically efficient synthesis. Hy- drazinolysis of I, followed by acidification with lamine. The crystalline DL-penicillin V potassium hydrochloric acid, produced t-butyl ~-a-4-car- salt showed 51.4% (514u/mg.) of the bioactivity hoxy-5,5-dimethyl- a-amino -2-thiazolidineacetate of natural penicillin V, indicating that L-penicillin hvdrochloride (11), Cl2H&zOnSC1, in 85% yield; V has little, if any, antibiotic activity. Cycliza- m.p. 172" dec. [Found: C, 43.83; H, 7.18; C1, tion of the penicilloate also was effected, but in lower yield, by ethoxyacetylene and a ketenimine 10.87; CX~~D+ 111" (c, 1 in methanol)]. Phenoxyacetyl chloride and triethylamine con- (pentamethyleneketene cyclohexylimines). It is verted I1 to a-t-butyl D-a-phenoxymethylpenicil- interesting to note that the entire reaction se- hate (III), Cd&sN&S, in 75% yield; m.p. quence starting with penicillamine was conducted 120-122' dec. [Found: C, 56.85; H, 6.86; N, at or below room temperature. Ci.Ti9; aZ5D+ 67" (c, 1 in methanol)]. Cleavage We are indebted to Bristol Laboratories of of the t-butyl ester with dry hydrogen chloride, Syracuse, NX., for financial support, to Merck and Co., Inc., of Rahway, N. J., for the preparation (1) J. C. Sheehan and G. P. Hess, THISJOURNAL, 77, 1067 (1965). (2) Penicillamine and 2-benzyl-4-methoxymethylene-5-(4)-oxazolone (6) Kindly furnished by Eli Lilly & Company, Indianapolis, Ind. condense to form trace amounts (0.03 to 0 08% by bioassay, 0.008% (6) Synthetic potassium penicillin V had a potency of 1078 dmg. i isolated) of penicillin G (benzylpenicillin). For a recent review of this 1Oyo (107.870 i lOYc) compared to standard natural penicillin V in a reaction see Karl Folkers in "Perspectives in Organic Chemistry," plate diffusion assay carried out under the supervision of Dr. J. Lein, Sir Alexander Todd, Editor, Interscience Publishers, Inc., New York, Bristol Laboratories, Syracuse, N. Y. N. Y.,1956, p. 409. (7) E. Brand1 and H. hiargreiter, Ostew. Chenz. 2.. 65, 11 (1954). (3) J. C. Sheehan and D. A. Johnson, THISJOURNAL, 76, 168 (8) Directions for the preparation of this ketenimine were fur- (1954). nished by Dr. C. L. Stevens, TVayne University. private communica- (4) J. C. Sheehan and P. A. Cruickshank, ibid., 78, 3677 (1956). tion. March 5, 1957 COMMUNICATIONSTO THE EDITOR 1263 of substantial quantities of certain key interme- 935. diates and to Mr. Sergey V. Chodsky for technical c, assistance. $34- 3.3- DEPARTMENTOF CHEMISTRY JOHN C. SHEEHAN < a MASSACHUSETTSINSTITUTE OF TECHNOLOGY CAMBRIDGE39, MASS. KENNETHR. HENERY-LOGAN 63.2- RECEIVEDFEBRUARY 11, 1957 is- THE SALT EFFECT IN THE AROMATIC NUCLEOPHILIC SUBSTITUTION REACTION' & Sir : The effect of added neutral salts upon the veloc- ity of the second order of the ion-dipole aromatic nucleophilic substitution reactions of lithium, SO- dium and potassium methoxides with 2,4-dinitro- chlorobenzene has been investigated at 25". The rates were studied in absolute methanol solvent as a function of reactant (LiOCHs, NaOCHa, and KOCH3) in the presence of added cations (Lif, Na+, and K+) and added anions (C2H-02-, I-, Br-, C104-, C1-, and NO9-). The reaction of NaOCH3 in the presence of added LiC104.3HzO also was studied in a 50 volume % methanol- benzene solvent. I .9; For reactions without added salts, the rate con- 1.81 stants (1 mole-' sec.-l) were: LiOCHI, 0.0242; 0.0 0.025 0.05 0.10 0.15 0.20 NaOCHS, 0.0262; KOCH3, 0.0278. A consistent MOLARITY OF ADDED' SALT. pattern of salt effects is typified by the data for the LiOCH3 reaction shown in Fig. 1. At low concen- Fig. 1.-Lithium methoxide and 2,4-dinitrochlorobenzene. trations of added salt, each cation exhibits a.n in- sociation occurs for LiOCH, than for KOCH3 or dividual effect, added to that of the cation intro- NaOCH3 in methanol. Potassium salts are strong duced along with the reactant methoxide. The electrolytes in methanol with dissociation con- anions cause an additional secondary effect. The stants of about 0.1 to 0.0Z5 It is known that reaction rate increases for acetate > C1-, Br- > potassium salts are stronger electrolytes than are I-, NOS- > Clod-. Salt effects are more pro- lithium salts in acetone.6 If a similar order of nounced in solvents of lower dielectric constant. electrolyte strength holds for methanol solutions, The observed effects cannot be correlated with then the effect of added potassium salts on the changes in ionic strength of the reaction medium LiOCH3 Li+ + -OCH3 equilibrium would be to as found by Bolto and Miller.* supply anions which would tend to associate more A qualitative explanation of the effect of lithium readily with Li+ so that the equilibrium would be salts assumes the equilibrium shifted to provide a greater concentration of OCH3-. LiOCH3 If Li + + -0CH3 This accounts for the increase in rate of the reac- The addition of a salt providing Li+ as a common tion. Sodium salts are not as effective as potas- ion should shift this equilibrium to decrease the sium salts, and the anion effects are consistent with concentration of the reactant, OCH3-. Since the those observed in the presence of Li+ alone. effective concentration of added Li+ will depend (5) E. C. Evers and 8. 0. Knox, THIS JOURNAL, 73, 1739 (1951). on the degree to which it remains associated with (6) J. F. Dippy, H. 0. Jenkins and J. E. Page, J. Ckem. Soc., 1368 the added anion, the rate will differ with different (1939). added salts. This assumes that the ion pair reacts JOHN D. REINHEIMER WILLIAMF. KIEFFER at a negligible rate compared to that for the ion. THE COLLEGEOF WOOSTER STANLEYW. FREY A similar interpretation has been used to account ~T'OOSTER, OHIO JOHN C. COCHRAN for the variation in rate of decarboxylation of tri- EDWARDW. BARR chloroacetic acid.3 The observed effect of anions on RECEIVEDNOVEMBER 16, 1956 reaction rate thus can be interpreted to suggest that the order of attraction for lithium ions in THE EFFECT OF NITRATE ION ON THE YIELD OF methanol is Ac- > C1-, Br- > NO3-, I- > Clod-.
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