[CONTRIBUTION FROM THE WILLIAM
H. NICHOLS LABORATORY, YEW Y O R K UNIVERSITY ]
THE SYKTHESIS AND PROPERTIES OF OCTOPINE AND ITS DIASTEREOISOMER, ISO-OCTOPINE' ROBERT M. HERBSTa
AND
E. ACGGSTUS SW.4RT3
Received March 4, 1946
The asymmetric influence of an optically active grouping upon the configuration of a second optically active grouping entering a molecule has long been recognized. However, the effect of external conditions in modifying this influence has not received much attention. In most instances where a second asymmetric group has been introduced into an optically active compound, the conditions favoring the synthesis have not been amenable to wide variation. At other times, it has not been feasible to work with an optically active form so that the resulting product was a mixture of racemates. An interesting modification of the latter type was the synthesis developed by Manske and Johnson for ephedrine (1,2) and certain of its analogs, wherein both asymmetric groups were introduced during a single catalytic hydrogenation. A number of years ago an amino acid derivative, octopine (I), was isolated from various marine organisms (3,4). On the basis of subsequent investigations by Akasi (5,6) and Wilson and his co-workers (4,7) octopine (I)was assigned the structure of an arginine-a-propionic acid derivative. Its synthesis from I ( +)arginine and a-bromopropionic acid was described by Akasi (6) and Ackermann and Mohr (8) and again by Irvin and Wilson (7) who used the esters of arginine and a-bromopropionic acid. Soon thereafter Knoop and Martius (9) described he synthesis of an octopine by the catalytic hydrogenation of a mixture of I ( +)-arginine and pyruvic acid in aqueous solution.
NH
NH
II
CHzNHCNHz
! C Hz !
CHz
I CHNH2 I
COOH
NH I
II
CHzNHCNH2
CH~NH~SH.
CH2
CH,
CH2 cH3 (Hd c I CH-YH-CH
CH2
COOH
COOH
1
CH
+ BrCH I I
COOH
I
- + I
I
I
COOH
i
I
I CHNH, I
CH3
+ CO : I
COOH
(1) During the synthesis of octopine by the method of Knoop and Martius it seemed likely that a second product, diastereoisomeric with octopine should be formed, although the authors had reported the isolation of only a single product. 1 Abstracted from a thesis presented by E. Augustus Swart t o the faculty of New York University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 2 Present address, E. Bilhuber, Inc., Orange, N. J. 3 Present address, Squibb Institute for Medical Research, Kew Brunswick, N. J. 368
SYNTHESIS OF OCTOPINE A S D ISO-OCTOPINE
369
Akasi (10) had already reported the synthesis of both octopine and its diastereoisomer, iso-octopine, by interaction of I ( +)-arginine and a-bromopropionic acid, both as the racemate and as the optically active forms. The separation of the diastereoisomers was simple since octopine formed a very insoluble picrate while iso-octopine picrate was rather soluble in water. The procedure of Knoop and Martius was of particular interest to us, since it offered an opportunity to investigate i,he influence of an external factor such as the pH of the medium upon the proportions of octopine and iso-octopine formed by hydrogenation of a mixture of l(r)-arginine and pyruvic acid. However, certain difficulties were immediately encountered. No octopine picrate could be isolated from the reaction mixture. On the other hand, a product forming a very soluble picrate was present. This product was eventually isolated by means of its sparingly soluble salt with flavianic acid. In the face of this difficulty, it became desirable to repeat the synthesis of octopine and iso-octopine by Akasi's procedure. In order to avoid the tedious precipitation of these products with phosphotungstic acid to free them from inorganic ions, Akasi's procedure was modified to the extent of substituting barium hydromde for sodium hydroxide to maintain an alkaline environment during the interaction of I ( +)-arginine and dl-a-bromopropionic acid. Both octopine and iso-octopine were isolated from the reaction mixture, the former by means of its insoluble picrate, and the latter by means of its sparingly soluble flavianate. The octopine so obtained was in every way identical with the product obtained from natural sources, a sample of which was made available to us through the kindness of Dr. D. W. Wilson. On the other hand, the properties of the iso-octopine isolated from the reaction mixture failed to correspond with the description given in the literature (10) for this product. It was, however, identical with the material synthesized by the Knoop and Martius procedure. In view of these developments, it became imperative to determine whether the compound isolated by us was iso-octopine and to verify the properties ascribed to it in the literature. Efforts to study the effect of pH upon the proportions of octopine end iso-octopine formed in the Knoop and Martius synthesis were therefore temporarily abandoned. Akasi (10) has described iso-octopine as a colorless product crystallizing from aqueous alcohol with two molecules of water of crystallization and melting at 158-159'. Its specific rotation in water was reported as $25.77". The picrate was described as fine yellow needles, melting at 198", and showing moderate water-solubility. Our iso-octopine contained no water of crystallization, melted with decomposition at 258-259", and gave a rather soluble picrate melting with decomposition between 190" and 195' depending on the rate of heating. The specific rotation of our product in water mas +25'. As claimed by Akasi, both octopine and iso-octopine give a positive Sakaguchi test, the color being purple rather than orange-red as in the case of arginine. Both products fail to liberate nitrogen in the van Slyke amino-nitrogen determination. It is interesting to note that octopine, m.p. 270-271' with decomposition, does not depress the melting point of iso-octopine. The melting point of the mixture is generally the same
370
R. M. HERBST AND E. A. SWART
or just slightly higher than that of iso-octopine. The melting points of both compounds may vary considerably depending on the rate of heating, due to the accompanying decomposition. Therefore, comparisons should always be made by simultaneous observation of the melting points in the same bath. Similar behavior was observed with derivatives of both compounds, so that melting point comparisons should be interpreted with caution. It had been shown that octopine, on oxidation with barium permanganate by the technique applied to arginine by Kutscher (11))gave as products carbon dioxide, acetaldehyde, and y-guanidinobutyric acid. Our iso-octopine prepared either by the modified Akasi method or by the Knoop and Martius method when oxidized in this manner was broken up into carbon dioxide, acetaldehyde, and
20 0
n
tl v +
15
5
0 5 MOLES NaOH per MOLE OCTOPINE
HCI
FIG. 1. THEEFFECTOF HYDROCHLORIC ACIDAND SODIUM HYDROXIDE ow ROTATION OF NATURAL OCTOPIKE (WILSON)
TRE
SPECIFIC
y-guanidinobutyric acid. The latter product mas identical with a sample prepared by the oxidation of arginine. Apparently the material isolated by Knoop and Martius for which they give the melting point as 261' and described by them as octopine was actually isooctopine. Their error in identification can be attributed to &mi's incorrect description of the characteristic properties of iso-octopine. h i had further attempted t o characterize octopine and iso-octopine by the effect of alkali and acid upon their rotations in aqueous solutions following the technique of Lutz and Jirgensons (12). The curves for the changes in rotation exhibited by these compounds upon addition of acid and alkali are rather incongruous as represented by Akasi. Reinvestigation of these effects gave entirely
371
SYKTHESIS OF OCTOPINE AND ISO-OCTOPIKE
different results in our hands. The curves for both compounds (Figures 2 and 3) are qualitatively very similar but show pronounced quantitative differences, Both compounds show two points of maximum rotation and two points of minimum rotation, the changes in rotation being markedly greater for iso-octopine than for octopine. A similar curve for natural octopine (Figure 1) agreed in every respect with the curve for synthetic octopine. The curves for changes in rotation of iso-octopine prepared by the Knoop method or the modified Akasi method were identical. Both Akasi and later Karrer and his co-workers (13) have speculated on the configuration of the propionic acid portion of octopine. The latter authors have retracted their conclusions, while those of the former are open to criticism on the
20
10
5
0
5
MOLES NaOH per MOLE OCTOPINE
HCI
FIG. 2. THE EFFECTOF HYDROCHLORIC ACID AND SODIVMHYDROXIDE ON OF SYNTHETIC OCTOPINE (METHOD B) ROTATION
THE
SPECIFIC
grounds of failure t o take into consideration the probable occurrence of Walden inversions. Akasi found that octopine was formed by interaction of I(+)arginine and I( - )-a-bromopropionic acid, while iso-octopine resulted from I( +)arginine and a(+)-a-bromopropionic acid. From this he concluded that octopine had I1 configuration while iso-octopine possessed the Id configuration although Fischer (14)had demonstrated that the a-bromopropionic acids undergo a Walden inversion upon reacting with ammonia, and Abderhalden and Haase (15) had shown the same t o be true during imino-dicarboxylic acid formation with glycine. Although it is tempting to speculate on the basis of Akasi’s synthetic work and the new rotation curves as t o the configuration of the octopines, the question must
372
R. M. HERBST AND E. A. SWART
remain unsettled for the present. Both compounds contain asymmetric carbon atoms comparable to those of arginine and alanine. The configuration of the arginine moiety is established by the synthesis of both compounds from l(+)arginine without involvement of the asymmetric carbon atom. Only the configuration of the alanine carbon atom remains in question. It appears likely from a consideration of the rotation curves and the van’t Hoff principle of optical super-position that octopine has the Id configuration while iso-octopine has the 11 configuration, although unequivocal proof is lacking. The natural occurrence of certain amino acids in the d-configurational form, although not common, is not
25
-
20 -
-
0
-
CI
’d
+
15
FIG. 3. THE
-
I
)
I
I
I
[
l
i
-
-
-
T 5
SPBCIPIC
unusual, hence the d configuration of the alanine moiety of octopine cannot be ruled out on the basis of the natural occurrence of this compound. Of interest waa the isomer designated as P-octopine by Akasi in view of its reputed synthesis from I ( +)-arginine and p-bromopropionic acid. Such a compound would exhibit all the functional groups of the octopines but contain only one asymmetric carbon atom, thus making its rotation curve particularly interesting. From Akasi’s description of this compound, it possesses many of the characteristics of octopine, and even the curve representing changes in rotation effected by acids and bases as observed by Akasi bears great similarity t o our curve for octopine. We were unable to synthesize this compound. Mixtures of arginine and P-bromopropionic acid showed no inclination t o react under the
SYhTHESIS OF OCTOPINE AND ISQ-OCTOPISE
373
conditions used for synthesis of the octopines, as evidenced by unchanged van Slyke amino-nitrogen content of the reaction mixtures. One is tempted to wonder whether Akasi's P-bromopropionic acid may not have been contaminated with the alpha isomer. In order to obtain a compound carrying all of the functional groups of the octopines but having only a single asymmetric carbon atom, E(+)-arginine was condenseld with chloroacetic acid under the conditions employed in the octopine synthesis.
NH
NH
I1
I1
CHzNHCnTHz
CH2NHCKH2
CHz I CH:!
CHs
I
I
CHKH2
i
COOH
+
ClCHz -+
I
COOH
I
CH-NH-CHZ
I
COOH
I
COOH
I1 The product, for which the name desmethyloctopine (11)is suggested, is a colorless, crystalline solid melting at 281-282" with decomposition and bearing great similarity to the octopines. Like the octopines, it gives a purple color in the Sakaguchi test and fails to liberate nitrogen in the van Slyke amino-nitrogen determination. The effect of the addition of acid or base to its aqueous solutions upon its rotation (Figure 4) is, however, qualitatively quite different from that observed with the octopines. In this respect it is also interesting to note that the rotation curve differs quite markedly from that of I(+)-arginine (16). The effect of addition of the acetic acid residue and the new functional group it carries places the rotation curve rather midway between that of arginine and the octopines. The authors wish to acknowledge gratefully the gift of a generous sample of natural octopine by Dr. D. W. Wilson of the University of Pennsylvania. EXPERIMENTAL
l(+)-Arginine monohydrochloride was isolated from a gelatin hydrolysate as the insoluble flavianate (17). The flavinate was decomposed by continuous extraction of its suspension in warm dilute hydrochloric acid with n-butyl alcohol. Arginine remained in the aqueous acid solution from which i t was isolated as the monohydrochloride by precipitation with pyridine after decolorization, concentration, and dilution with ethanol. Hunter's (18) method of purification was followed. Anal. Calo'd for CsHI5ClKaO2:N, 26.6. Found: N, 26.7, 26.5 (Micro Kjeldahl). [CY $25.2" ]: for arginine monohydrochloride in 3.5 normal hydrochloric acid ( c = 21; 1 = 1 dm.). Z(+)-ATginine carbonate was isolated by the method of Kossel and Gross (19) after decomposition of arginine flavianate according t o Felix and Dirr (20). Flavianic acid was prepared from Naphthol Yellow S (17). Pyruvic acid was redistilled under reduced pressure frequently, and stored in the icechest.
374
R. Me HERBST AND Ea Ai SWART
Zso-oclopine ( A ) [Knoop and Martius Method (9) 1. A solution of 4.2 g. of l(+)-arginine monohydrochloride and 1.36 ml. of pyruvic acid in 25 ml. of water was neutralized to litmus by addition of saturated barium hydroxide solution, after which a second equivalent of pyruvic acid (1.36 ml.) was added. The solution was hydrogenated with palladium oxide catalyst (21) a t a hydrogen pressure slightly over atmospheric. After about thirty hours, hydrogen absorption was negligible and van Slyke determinations indicated that 85-90y0 of the arginine amino nitrogen had disappeared. After acidification with a slight excess of sulfuric acid and removal of the barium sulfate, unreacted arginine was removed by the addition of a slight excess of flavianic acid. After concentrating the filtrate from the arginine flavianate to about 75 ml., iso-octopine flavianate was isolated upon addition of excess flavianic acid and chilling. After recrystallization from water, iso-octopine flavisnate meltedlat 206-207" with decomposition.
30
20
5
0
5
HCI MOLES NaOH per MOLE DESMETHYLOCTOPINE FIG.4. THEEFFECT OF HYDROCHLORIC ACID AND SODIUM HYDROXIDE ON ROTATION OF DESMETHYLOCTOPINE
THE
SPECIFIC
The flavianate was decomposed by suspension in a small amount of hot water and grinding with hot saturated aqueous barium hydroxide solution and filtering. After repeating this treatment with the insoluble material, barium ion was quantitatively removed from the combined filtrates by careful addition of sulfuric acid. The resulting solution of isooctopine was decolorized with charcoal, concentrated to a syrup under reduced pressure and treated with 40-50 ml. of ethanol. The iso-octopine separated as a colorless solid which crystallized from 70y0 ethanol as clusters of fine, glistening needles, m.p. 258-259' with decomposition. (Satural octopine, simultaneously in the same bath, melted at 270-271", with decomposition.) A n a l . Calc'd for C B H I ~ N I ON, ~ : 22.75. Found: N, 22.5, 22.5 (Micro Kjeldahl). 24.5 +25" in 2.5% aqueous solution in a semi-micro 1 dm. tube. [aID The same product resulted when I(+)-arginine carbonate, as directed by Knoop and Martius, was used in place of the monohydrochloride. Ozidation of iso-octopine. An aqueous solution of 1 g. of iso-octopine w m treated with a solution of a slight excess of barium permanganate. The reaction mixture wm aerated for
SYNTHESIS OF OCTOPINE AND ISO-OCTOPINE
3i5
two hours a t 40°, the exhaust air passing through sodium bisulfite solution. Barium ion was removed quantitatively by careful addition of sulfuric acid after filtering off the precipitated manganese dioxide. The resulting solution was evaporated to a small volume under reduced pressure, treated with 15 ml. of concentrated hydrochloric acid, and the volume again reduced to about 2-3 ml. On chilling, y-guanidinobutyric acid hydrochloride crystallized. After recrystallization from a small volume of dilute hydrochloric acid, the material melted a t 184-185", and showed no depression when mixed with y-guanidinobutyric acid hydrochloride obtained by oxidation of arginine (11). The sodium bisulfite solution wm distilled after addition of excess sodium carbonate. From the distillate, acetaldehyde was isolated as the dimedon derivative, m.p. 141-142", showing no depression when mixed with an authentic sample. Octopine and iso-octopine ( B ) [Akasi Method (10) 1. Two modifications of the procedure m*ere introduced, the volume of the solution was reduced to about 25% of that specified by Akasi, and barium hydroxide replaced sodium hydroxide to maintain a n alkaline reaction in the solution. A sallution of 11.4 g. of I(+)-arginine monohydrochloride and 7.6 g. of dl-a-bromopropionic acid in 200 cc. of water was made alkaline by the addition of 31.5 g. of crystalline barium hydroxide. After keeping at 37" for 72 hours the amino-nitrogen content of the solution indicated that 80% of the arginine had reacted. Barium ion and unreacted arginine were removed as described above, while excess flavianic acid was removed by extraction with butyl alcohol. The arginine-free filtrate was treated with a hot saturated aqueous solution of picric acid equivalent to the octopines present. On concentrating the solution under reduced pressure the red picrate of octopine crystallized. After two recrystallizations from water it melted a t 222-222.5' Kith decomposition. Octopine was liberated from the picrate by treating its hot aqueous solution with a n excess of 6 N sulfuric acid and extracting the picric acid with ether. After quantitative removal of the sulfate ion with barium hydroxide, the solution n a s evaporated to a thin syrup. Addition of ethanol precipitated the octopine as a colorless solid, which after two recrystallizations from 70y0 ethanol melted at 262-263' with decomposition. (Simultaneously in the same bath natural octopine melted a t 262-263' with decomposition.) Anal, Calc'd for CgH&',O4: N, 22.75. Found: N, 22.9 (Micro Kjeldahl). [a: :1 +20° in 2.5% aqueous solution in a semi-micro 1 dm. tube. The filtrate from the precipitation of crude octopine picrate was acidified with sulfuric acid, and extracted with ether to remove picric acid. After quantitative removal of sulfate ion from the solution, iso-octopine was isolated as the flavianate as described above. The product obtained by decomposition of the flavianate crystallized from 70% ethanol as clusters of fine, glistening needles, m.p. 258-259" with decomposition. (Simultaneously in the same bath iso-octopine (A) melted at 258-259" with decomposition.) The air-dried product failed t o lose weight on drying a t elevated temperatures or in vacuum, and no other evidence of water of crystallization could be obtained. Anal. Calc'd for CgHlsN404: Tu', 22.75. Found: N, 22.6 (Micro Kjeldahl). [a]: +25" in 2.5% aqueous solution in a semi-micro 1 dm. tube. p-Octopine. An attempt was made to condense Z(+)-arginine with p-bromopropionic acid following closely the conditions described by Akasi (10) in one experiment, and our own in a second. I n both cases van Slyke amino-nitrogen determinations failed t o indicate the disappearance of arginine and this reactant could be recovered quantitatively as the flavianat e. Desmethyloctopine (ZZ). A solution of 4 2 g. of Z(+)-arginine monohydrochloride and 3.8 g. of monochloroacetic acid in water was treated with 30 ml. of 0.1 2cf sodium carbonate solution and diluted t o 330 ml., after which it was boiled under reflux for four hours, when 90% of the amino nitrogen (van Slyke) had disappeared. As the reaction proceeded, the color given in the Sakaguchi test changed from the orange characteristic of arginine t o a purple similar to that given by octopine. After acidification of the reaction mixture t o
376
R. M. HERBST AND E. A. SWART
Congo Red with hydrochloric acid and removal of unreacted arginine as the flavianate, the solution was evaporated t o a thin syrup under reduced pressure. Addition of ethanol precipitated the product, which was redissolved in 70% ethanol acidified with hydrochloric acid, and reprecipitated by addition of pyridine. After two recrystallizations from 70% ethanol, the product melted at 281-282" with decomposition. It gave a purple color in the Sakaguchi test and was only moderately soluble in cold water. N,O24.14. ~: Found: N, 23.9,23.9 (Micro Kjeldahl). Anal. Calc'd for C ~ H I ~ N ~ [CY]: $24" in 2.5% aqueous solution in a semi-micro 1 dm. tube. Rotation curves. All solutions for determination of specific rotations were freshly prepared by weighing amounts of each compound sufficient to prepare a tenth molar solution into calibrated 2 ml. volumetric flasks, adding the calculated amount of standard hydroTABLE I CHANGE OF ROTATION ON ADDITIONOF ACID OR ALKALI TO NATURAL AKD SYNTHETIC AND DESYETHYLOCTOPINE OCTOPINE.ISO-OCTOPINE
I
I
OCTOPINE
ISO-OCTOPINE
-~ a
[ . I D
OL
OL
OL
1
]
a
LalD
2.4 $0.47 +20 +0.49 $20 $0.63 +25 +0.62 $25 2.51-kO.61 $24 _-------__/-
Approx. 0.1 M solution
Moles HC1:mole substance 0.5:1 1:l 2:l 3:l 5:l 1O:l
2.4 $0.41 2.5 $0.43 2.4 +0.45 2.5 f0.47 2.5 $0.48 2.5 +0.49
+17 4-17 $0.42 +19 $0.47 4-19 $0.47 $19 4-0.48 +2@ +0.48
2.5 $0.41 2.4 $0.33 2.4 $0.32 2.4 $0.32 2.4 $0.34
$16 +14 $0.37 +15 $0.28 +I1 $0.26 $102.5 $0.59 $13 4-0.36 +14 $0.22 $9 f0.23 $92.5 $0.63 +13 $0.34 +14 $0.23 +9 +0.23 4-92.6 $0.65 4-14 $0.38 4-15 $0.27 f l l $0.24 $102.5 $0.66
+17 $19 +19 +19 $19
$0.48 f0.46 f0.53 $0.52 $0.53
4-19 $0.48 $192.6 $0.56 f18 f0.45 $182.5 4-0.49 4-21 $0.50 t-202.5 4-0.52 +21 +0.52 4-21 2.5 $0.52 +21
4-22 4-20 f21 4-21
Moles Na0H:mole substance 0.5:l 1:l 2:l 3:l 5:l c
t P
[&,
f24 f25 $25 +26
= grams of solute per 100 ml. of solution = temperature in degrees centigrade = observed rotation in degrees = specific rotation, in degrees, at the given temperature
chloric acid or sodium hydroxide solution and diluting to the mark. Rotations were determined in a 1 dm. semi-micro tube in a Schmidt and Haensch half-shadow polarimeter, using a sodium vapor lamp as a source of monochromatic light. Each rotation was the average of ten consecutive readings and the average deviation was f0.02". Since the observed rotations were all less than unity, specific rotations are not significant beyond the nearest whole degree as reported in the table. The pertinent data are recorded in Table I. SUMMARY
1. The catalytic hydrogenation of a mixture of ,!(+)-arginine and pyruvic acid in aqueous solution proceeds asymmetrically with the formation of iso-octopine, a diastereoisomer of octopine.
SYNTHESIS OF OCTOPIKE AND ISO-OCTOPINE
37i
2. The characteristic properties of iso-octopine have been described and its structure has been established by its oxidative degradation to y-guanidinobutyric acid and acetaldehyde and by its synthesis together with octopine from l(+)arginine and db-a-bromopropionicacid. 3. The synthesis of desmethyloctopine from I ( +)-arginine and monochloroacetic acid has been described. 4. The effect of acid and alkali upon the specific rotation of natural and synthetic octopine, iso-octopine, and desmethyloctopine has been determined. 5. It is suggested that the a-propionic acid residue has the d configuration in octopine and the 1 configuration in iso-octopine. NEW YORK,N. Y. REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)
MANSKE AND JOHNSON, J . Am. Chem. IS”.,61,580 (1929). MANSKE AND JOHNSON, J. Am. Chem. Soc., 61, 1906 (1929) ,MORIZAWA, Acta schol. med. uniw. imp. Kioto, 9, 285 (1927). MOOREAND WILSON,J. B i d . Chem., 119, 573 (1937). ABASI,J . Biochem., Japan, 26, 261 (1937). ARASI, J. Biochem., Japan, 26, 281 (1937). IRVIN AND WILSON,J . B i d . Chem., 127, 555 (1939). hCRERM.4NN AND MOHR,2.physiol. Chem., 260, 249 (1937). KNOOPAND MARTIUS,2. physiol. Chem., 268, 238 (1939). AKASI, J. Biochem., Japan, 26, 291 (1937). KUTSCHER, 2.physiol. Chem., 32, 413 (1901). Lurz AND JIRGENSONS, Ber., 63,448 (1930); 64,1221 (1931). KARRER,KOENIGAND LEGLER, Helv. Chim. Acta, 24, 127, 861 (1941); KARRERAND APPENZELLER, Helv. Chim. Acta, 26, 595 (1942). FIBCHER, Ber., 40, 489 (1907). ABDERH.4LDEN AND HASSE,2.physiol. Chem., 202, 49 (1931). HERBST AND GROTTA, J. Org. Chem., 11,363 (1946). Org. Syntheses, Coll. Vol. 11, 49, (1943). HUNTER, J. B i d . Chem., 82, 731 (1929). KOSSEL AND GROSS, 2.physiol. Chem., 136, 167 (1924). FELIXAND DIRR,2.physiol. Chem., 176, 38 (1928). Org. Syntheses, Coll. Vol. I, 2nd Edition, 463, (1941).
