Sept., 1941)
NOTES
3245
The data presented in Table I pertain to this observation. It can be seen from the table that PGA deSince this paper was submitted, R. M. Garrels and F. T. Gucker have published a valuable study of aqueous composes a t a regular rate on incubation a t 30'. lead chloride solutions [Chem. Rev., 44, 117 (1949)l. A very great rate of decomposition occurs in the These authors give considerable additional evidence for sterile medium which has been generally used for incomplete dissociation in such solutions, and derive the growth of Lactobacillus arabinosus 17-5. I n values for K of about 0.03 from e.m.f. and conductance this medium, 6.1s to 14.54 pg. of diazotizable data. amine calculated as 9-ABA per 1000 pg. of PGA UNIVERSITY OF GLASGOW RECEIVEDJANUARY 31, 1949 are liberated during an incubation period of from GLASGOW, SCOTLAND forty to sixty-four hours. The diazotizable component liberated in this medium is significantljThe Liberation of Diazotizable Amine from greater than the amounts liberated in either aqueous or neutral phosphate buffer solutions of PGA. Pteroylglutamic Acid1 These results indicate that certain substances in BY B. KOFTAND M. G. SEVAG the sterile medium accelerate the decomposition During a study of the possible role of pteroyl- of PGA. The nature of these substances is under glutamic acid (PGL4) and @-aminobenzoic acid investigation. (p-ABA) on the inhibition by sulfonamides of the DEPARTMENT O F BACTERIOLOGY OF MEDICINE growth of Lactobacillus arabinosus strain 17-5 and SCHOOL other bacteria, certain inconsistancies have been UNIVERSITY O F PENNSYLVANIA RECEIVEDMAY16, 1949 PA. observed by us. These inconsistencies suggested PHILADELPHIA, the possibility that pteroylglutamic acid was undergoing decomposition in the sterile medium. Lithium Borohydride as a Reducing Agent Certainly, if this were so, i t would have considerable bearing on the interpretations of the results BY ROBERT F. NYSTROM, SAUL W. CHAIKINAND W E L D O ~ G. BROWN of physiological experiments with pteroylglutamic acid. Lithium borohydride shares with lithium aluTABLE 1 minum hydride the property of solubility in ether RATEOF THE DECOMPOSITION OF PTEKOYLGLI'TAMIC' A c ~ u and other organic solvents. I n ether solution it is a more powerful reducing agent than sodium boro(PGA) Y p g P-ABA/lOOO p g of P G A c - - - hydride (in water or alcohol solution) but is milder Pteroylglutamic acid 0 20 40 64 180 1fiX than lithium aluminum hydride. This combinasolutions" hr. hr. hr. hr. hr hr. tion of properties, together with the prospect of 1 Distilled water h r o u g h t t o P H 7 . 0 1.62 3.00 3.91 6.36 9.09 11.82 early commercial availability, suggests useful ap2 M/30 phosphate plications for lithium borohydride particularly in buffer p H 7.3 1 . 7 2 2 . 7 3 4.27 6.36 9 . 5 4 12.3fi the execution of selective reductions. 3 M/30 Na2HPO4, pH Solid lithium borohydride has been known to 9.18 1.36 2.55 4.27 11.36 13.63 81.82 4 M/30 RHzPO4 PH flash on exposure to humid air, some samples being 4.5b 1.36 2.18 2.72 3.36 4.32 5.45 more prone than others, and for this reason trans5 Growth medium ( p H fers of the solid should be conducted in a dry at7.0) (used for L. mosphere. However, solutions of lithium boroarabinosusa) 2.50 3.82 6.18 14.64 18.86 45.44 6 Medium as in (5) hydride are relatively insensitive to moisture and without PGA 0 0 0 0 0 0 in the experiments to be described no special pre7 1 pg p-ABA/ml. of cautions were taken to exclude moisture. OtherM/30 phosphate buffer of p H 7.3 1 1 1 1 1 1 wise the procedures followed in lithium borohydride reductions were generally similar to those a All solutions were autoclaved for ten minutes a t 10 lb. pressure. Systems 1 to 5 contained 500 pg of PGA/ml. employed in reductions by lithium aluminum hyThe solutionsowere then kept in a constant temperature in- dride. Tetrahydrofuran proved advantageous as cubator a t 30 . * Pteroylglutamic acid dissolves on autoclaving and a precipitate forms on cooling; determinations a solvent, since more concentrated solutions of the p-ABA hydride could be used, viz., 3.5 111 as compared for p-ABA were made on uniform suspensions. content of the various systems were determined according with 0.5 A 1 in diethyl ether. to Bratton and Marshall4 using Klett-Summerson photoThe aldehydes and ketones (cf. Table I) were electric colorimeter with filter No. 54, 1 pg of p-ABA/lO reduced rapidly a t room temperature in exotherml. reaction system gives a colorimetric reading of 22. mic reactions whereas the esters reacted slowly and (1) This investigation was supported, in part, by a research the mixtures were heated to reflux for periods up to grant from the Division of Research Grants and Fellowships of the six hours. In the selective reduction of the ketone National Institute of Health, U. S. Public Health Service. groups of the keto-esters, and of m-nitroacetophe(2) The authors are indebted t o Dr. C. W. Waller, Lederle Lahoratories, Pearl River, New York, for a freshly recrystallized sample of none, ice-bath cooling was employed to enhance sePGA. It contained 1 pg of g-ABA/1000 pg of PGA. lectivity. The attempted selective reduction of (3) T. D. Luckey, G. M. Briggs, Jr., and C. A. Elvehjem, J . Biol. ethyl acetoacetate gave rise to a borate complex Chcm., 164, 157 (1944). from which the reduction product could not be (4) A. C.Brstton and E. IC, Marahdl, Jr., ibid., 118,637 (1939). equations of Wynne-Jones and Bjerrum are not applicable to this case.
