1'OTENTIAL A~NTIIIA1)IATIONDRUGS. 11
Soveiiiber 1963
763
TABLE I
x-(H Y U R o X Y A L K Y L ) . 4 C s l ' . ~ ~ l l ) ~ S so.
R:
Rl
B.p.,
3 4 5
7
, . .
S
...
Methodn
Formula
calrd.--.
---yo C
c
N
I1
found-€I
N
,
97 A CjHiiNOs 51.26 9.47 11.96 90 A C6H13N02 54.94 9 . 9 9 10.68 ... 76.5-77 93 A CiaHziN02 64.13 11.30 7.48 ?J-( 1,2-Dialkyl-2-hydroxyethyl)acetamide CH3CONHCHR1CHR20H 103-104(0.2) ... 99 A C ~ H I ~ N O 54.94 P 9.99 10.68
CH3
5%
c:
131 (0.1)c 133-134 ( 0 ,l ) d
6
CHa
(mm.) M p . , O C . Yield, c/o
~-(l-Alkyl-2-hydroxyeth).l)ace(xn~idt: (:H3CONHCItl11?CH?C)H 14ti-I48 ( 1 ) ... (i3 u CBHIJIL'O, 54.04 ! ) . W 1O.W 54.65 !l.7:3 10.3s >11S ( 0 . 6 ) S7.5-SS 4!) (:6H13?J0:: 54.!)4 !).09 10.68 35.21 ! ) . S O 10.71 127-1:32 ( 0 . 3 ) 03-64 '7'3 A CiHljNO, 57,OO 10.41 9 . 6 5 5s.51 IO. 38 !I, 74 135-138 ( 1 . 2 ) 84-85 06 A CiHljN02 57.90 10.41 9 . 6 j 58.65 10.81 9 . !)!J ... 82.5-83 90 A C~OHBINO?64.13 11.30 . . . 63.73 11.13 , , N-(2-Alky1-2-hydrosyetli~l)a~e~xiiiide CH3CONHCHzCHRlOH
II ClI3 H H H
I h
3
OC'.
,
.
50.72
11.!I2 10.62 7.31
54.83
9 . 9 3 10.65.
9.09 54.77 9.87 63.54 11.02
,
See Experimental Section for details. n 2 5 1.4687; ~ mentioned hiit not descaribed by A. X. Campbell and P. F. Tryon, Ind. Eng. ~ n Z 5 D 1.4660. n Z K1.4665; ~ B. T. Gillis [ J . o r g . Chem., 24, 1027 (1959)] used another synChenz., 45, 125 (1953). n z 61.4654. thesis and reported b.p. 112-115' (0.3 mm.), n~ 1.4664.
TABLE I1 THIAZOLINETHIOLS
THI.4ZOLINES AND
----"a
Yield,
KO. 101'
11 12 IS" 14' 15 16 17 18 19
20
It I
R%
H C2Hj
H H
H
H H CH3
CHa CH3 n-CZHi i-CaHi ?t-CsHia
H H
Ra
CHI H CzH, CH3
H H H
H n-C&j3 H H 4-3\Iethyl-2-thiaxoliiie-2-thiol 5-31ethyl-2-thiazoline-2-thioP H
"C.(inin.) 51 (20) 67 (20) 62-63 (16) .5-58 (20) 67 (49) 78-79 ( 2 0 ) 74-75 (20) 02-93 ( 2 ) SZ"(1.2) 98, 5-9gd 92-93d
lLp,,
?i%
1.4977 1.4960 1.4939 1.4900 1.4862 1.4920 1.4918
1.48.53 1.484i
...
...
7o 50 59
34 40
6.5 50 79 67 54 50 60
llorinnla
C
ca1cd.--
H
C ~ H Y N S 52.13 7.87 CGHIIIL'S 55 76 8 . 5 8 C I H I I ? ; ~ 55 76 8 48 CGHIIXS L5.76 8 . 5 8 C ~ H ~ I S 55 S 76 8 . 5 8 CiH13XS 58.69 9 . 1 5 58 69 C;H&S 9 15 CIOHIYNS 64.81 10.33 CloHlsXS 64.81 10.33 CIH,NS? , . , .,. C,H;XS;? .,. , . .
N
12.16 10.84 10.84 10.84 10.84 9.78 !).78 7.56 7.56 ...
...
-(Z C
found---
H
N
8 . 1 1 12.20 8 4 10.9 8 . 5 9 $),!IO 8 . 6 0 11.2 8 . 4 0 10.93 ! ) . 0 3 !).84 0.42 1 0 . 1 65.0 10.14 i . 4 1 ti4.75 10.26 7 . 8 ,.. ... ... ... ,..
$2.28 55.6 55.79 55.56 55.21 50.22 60.1
.
.
t
1'. A. S. Smith and J. 31.Siillivaii [ J . Org. Che?n., 26, I133 (lO61)] iised nii alieriitttive syiiihesis aiid reported h.1). 4s" (22 i n n i . ) . Lit.0b.p. 55-56' (26mm.). c A. I. Meyers and J. J. R.itter [ J . Org. Chem., 23, 1918 (1058)] used an alternative synthesis and reported Melting point. Prepared by a procedure siniilar to that of P. A. S. Smith and J. 31.Stillivaiia who reb.p. 146-148", ~ Z K D 1.4825. ported m.p. 93-95'. '1
h
hydrochlorides (Table 111) in high yield. In contrast, the hydrolysis of two 2-thiazoline-2-thiols (19 and 20) required 150 hr. for complete hydrolysis to the aminothiol. I n one such hydrolysis we detected the presence of a partially hydrolyzed intermediate (see Experimental Section). Radioprotective Activities.-The results tabulated i r i Tables IV and V were obtained exactly a': described i n our first paper.' The same standards for rating the compounds mere used. Our results with l-amino-2-i)ropanethiol (27) i n rodents corifirnied the observation of earlier workers3~,12,13that this i i an eff ectivc radioprotective Sub3taiice. I t s prophylactic range is 4 d 1 2 to be sui)erior to those of all other amiriothiol derivatives. Its distribution and elimination and its nietabolism products have been studied14 and papers describing its protective (12) D . W. van Bekkum and H . T. hl. Nieuwerkerk, Intern. J . Radiation Bioi., 7 , 4 i 3 11984). ( 1 3 ) L. I. Tank, .Wed. lindiol., 6, S o . 9. 34 f1980). (14) G. V. Kalistratov and E. F. Romantsev, Farmakul. i Toksikul., 27, 364 (1964).
actmionon lysogenic bacterial5 and yeastI6 have appeared. We also confirmed the earlier observation12 that the isomeric 2-amino-1-propanethiol (21) is inferior in the dose range studied. The isomeric aminobutanethiols 22 and 28 have beeii reported previ0usly3~~1~ to offer only fair protection i n rodents, and other structural variants in this group (23 and 30) produced no striking changes in protective activity. Among the higher homologs described here only 24 and 25 are of continuing interest. An isonier of 25, l-aniino-3-methyl-2-butanethio1, was reported3c*13to have fair protective activity. The octaiiethiols 26 and 29 are not protective even in bacteria. An earlier preparation of 29 was reported to have no protective activity." In earlier work's no significant relationship was found between the radioprotective activity of certain amino(15) N. N. Zhukov-Verezhnikov, I. N. hfaiskii, A. P. Pekhov, Ir;. I. Rybakov, P. P. Saksonov, B. A. hlishchenko, V. A. Kozlov, K. D. Rybakova, and E. D. Aniskin. Radiobiologiya, 4, 738 (1964). (16) J. Judis, J . Pharm. Sci., 50, 221 (1981). (17) F. I. Carroll, J. D. White, and h l . E. Wall, J. Org. Ckem., 28, 1236 (1063).
(18) V. \ V d f and W. Uraun, Arziieimittel-Pursch., 10, 304 ( l V U 0 ) .
.\ = :tcetonitrile, €3 = ethyl acetate, (J = ether, 1) = 2-prupaiiol cuntainiiig :i few tilops of HCI. ' Iudimetric in diliite HC'I. Prepared hy the hydrolysis of 4-methyl-2-thiazoliiie-2-thiol; see Experimeiital Sectioti. IJitj.3u m.p. 94'. 11. C i . T>awtoti, H. Saltzmaii and IT. 11. Martin (Report o n Anti-Radiation Driig Program, Divisioii of Fiiclear LIedicine, Walter lieed Army Iiist itiiirl of Research, April 1959) iised another synthesis biit did not desyribe the product. E . ( + , Lawtoil. ~t ~ l . used , ~ another synthesis u i l t l reported m.p. 186-188". 1 In early work we also used the procedure of S.Gabriel aiid E.Lerrpold [Ber., 31, 2832 (1898)l who 111-tlrolyzed 5-methyl-2-thiazoline-2-thiol and reported m.p. 87-88'; the optical resolritioii of this siibst,aiicve was reported by J . R. Piper and T. P. Johnston, J . Org. Cheni., 29, 1657 (1964); for commercial synthesis aiid is(j1atii)iisee 1;. Y. Patent 3,165,451 (l!)G5). S. I ) . Tiirk, R. P. Louthail, K. L. Cobb, aiid C. 11. Bressoii [ J . Org. Chenz., 27, 2852 (196211 iised another s p t h e s i s and reported m.p. 1 Prepared but not described in ref. 17. Free base, m.p. 82--Sti0; E. 1).Rergnxiiiik m d -1.Kalrmyner [Xec. trnz,. d i m . , 78, 157'. ( l95!j)l iised another synthesis and reported m.p. 78-80' for the free base. r
No.
10 II 12 I:: I4 I .5 lti 17 1s 1!)
Itadiation protection Bacteria Rodent test tpst (13. r o l l )
(;ootl
Fair
. . Nollc~
SOliC~
...
Fair Slight
...
(;ooti
. . . .
C;llud
Slight Slight Xorie
. . .. ..
Fair
20
1 hiol 1)iwursoi- m d thc c I tiiols I'u i ' i f t v . 111 a receiit studyi$ the failure of 22 I Iiiazoliii~~~~ to prot w t rodents TWS rel'orted atid siiiiilar failuics with thiazolines have beeii reported prv\-iouJy.3L1 lye have observed protective activity with eight of nine thiazolines studied (10-18). Of particular iiiterest was t'he observation that the t,liree thiazolines offcriiig good protect'ioii (10, 15, aiid 16) are the precursors of the three anhot'hiols (27, 24, and 25) found to 1)roviclv t h r hest I)roteotioii in the 1)rc
Sovciiiber 1963
1'OTESTIAL ANTIRADIATION
Experimental Section22 1-Arniiio-Zpropanol was Eastman material and 2-amino-2methyl-1-propanol was a gift from the Commercial Solvents Corp. l-Amin0-2-butano1,~~3-amino-2-butan01,~~2-amino-3and ~ ~ ~l-amino-2-0~~ methyl-l-butanol,25~2 - a m i n o - l - o c t a n 0 1 , ~ ~ tano127 were prepared either by catalytic reduction of the appropriate nitro alcohol or by reduction of or-amino acids by the activated XaBH4reagent of Brown and Subba Rao.2* Analogous reductions of amino acids b57 LiAlHI have been described previ0usly.~5 2-Amino-l-pentanol.-A solution of 83.6 g. (0.625 mole) of anhydrous A1C13 in 270 ml. of dry diglyme was added to a solution of 71.3 g. (1.88 moles) of NaBH4 in 550 ml. of dry diglyme. The mixture was stirred a t 70" while 117.1 g. (1.0 mole) of solid 2-aminopentanoic acid (Mann Research Laboratoriesj was added in portions during 2 hr. The reaction mixture was then heated on a steam bath for 3.5 hr. The pasty mass was poured onto crushed ice and acidified with concentrated HC1 to dissolve all solids. The solution was evaporated to dryness under reduced pressure, the residual solid was dissolved in water, and the solution was treated with excess 307, S a O H solution and finally saturated with potassium carbonate to cause the separation of 2-amino-1-pentanol as a supernatant layer; additional product was obtained by extracting the aqueous phase with n-butyl alcohol. The organic layers were combined, dried ( MgS04), and distilled to yield 82.4 g. ( 8 0 % ) , b.p. 96-98' (19 mm.), set ~ point about 23O, n z l 1.4508. Anal. Calcd. for C6H13KO: C, 58.21; H, 12.70, Tu', 13.58. Found: C, 58.25; H, 12.63; S , 13.50. 2-Amino-1-pentanol is very soluble in water. It forms a hydrochloride salt, n1.p. 90.5-91.5' (acetone-acetonitrile). A dibenzoyl derivative, 2-benzamido-1-pentyl benzoate, was prepared by the Schotten-Raumann procedure and obtained as colorless needles, m.p. 136.5-137.5" (ethanol). Anal. Calcd. for C19H21N03: C, 73.29; H , 6.80, ?;, 4.50. Found: C,73.44; H, 6.84; N, 4.43. This latter compound was refluxed for 5 niin. in 2 4 XaOH in 50% aqueous alcohol. The solution was allowed to cool and deposited the monobenzoyl derivative, N-[( 1-hydroxymethyljbutyl]benzamide, m.p. 96-97', needles from CCla. Anal. Calcd. for ClzH17N02: C, 69.53; H , 8.27. Found: C, 69.88; H , 8.64. N-iHvdroxvalkvllacetamides (Table I) are high-boiling vis. - cous liquids which usually crystallize on standing. T h e i are insoluble in ether or benzene but dissolve readily in water and alcohols. Solid substances were recrystallized from ethyl acetate in our work but we made no attempt to achieve a high degree of purity. Method A.-Acetylation of the amino alcohol by ethyl acetate involved a modification of the procedure of D'Alelio and Reid.' The amino alcohol was refluxed with 2 equiv. of ethyl acetate for 75-90 hr. and the mixture was then fractionally distilled, except in the case of 5 and 8 where the amide solidified in the pot and was then recrystallized from ethyl acetate. Method B.-Dehydration of the acetate salt of the amino alcohol, as described by Wenker,6 was used to prepare N-[(lhydroxymethyl)propyl]acetamide ( 1 ). Equimolar amounts of 2-amino-1-butanol and glacial acetic acid were stirred and gradually heated while water escaped through a simple still head. When the reaction mixture reached 205", the product was collected by fractional distillation at reduced pressure. When the temperature was allowed to exceed 205", increased amounts of 4ethyl-2-methyl-2-oxazoline (see below) were obtained as a forerun in the distillation. When this procedure m-as used for the acetylation of 2-amin0-2-methyl-l-propano1, the oxazoline was the only product isolated (see below).
(22) All melting points and boiling points are corrected: analyses \\-ere performed b y S. 31. Nagy (Massachusetts I n s t i t u t e of Technology) or b y C. K . Fitz (Needham. M a s s . ) . (23) R . Ghirardelli and H. J. Lucas, J . A m . Chem. Soc., 79, 734 (1957). (24) C. A. Vander W'erf. R . Y . Heisler, a n d W. E. McEwen. ibid., 76, 1231 (1954). ( 2 5 ) ( a ) 0. Vogl and &I. l'bhm, .Ifonatah., 83, 541 (1952); (b) ihid., 84, 1097 (lY5i3). (26) R . J. Dummel and E. A . Garlock, J . Org. Chem., 27, 1049 (1962). (27) W.C. Gakenheimer and W. H. H a r t u n g , ibid., 9, 85 (1944). (28) H . C. Brown a n d B. C. Subba Rao, J . Am. Chem. Soc., 78, 2582 (1956).
DRUGS. 11
765
Method C.-Acetylation of the amino alcohol by acetic anhydride was used t o prepare N-( l,l-dimethyl-2-hydroxyethyljacetamide (2). 2-Amino-2-methyl-1-propanol was stirred a t 80-90' while an equimolecular quantity of acetic anhydride was added during 15 min. The reaction mixture was distilled at reduced pressure. The material which did not distil below l l 8 O (0.6 mm.) solidified on standing in the pot and was then recrystallized. During the distillation a fraction b.p. 92-97' (1 mm.) deposited a 12% yield of the acetate salt of 2-amino-2-methyl-lpropanol, m.p. 109"; the same substance was prepared independently by the neutralization of the amino alcohol with acetic acid in acet,onitrile solution. Anal. Calcd. for CGH~SXOI: C, 48.30; H, 10.13; N, 9.39. Found: C,48.32; H, 10.15; N,9.25. When this method of acetylation was applied to 2-aniino-3methyl-1-butanol both X- and 0-acetylation occurred to give 2-acetamido-3-methyl-1-butyl acetate, b.p. 111-114" (0.2 mm.), n Z 51.4528. ~ Anal. Calcd. for CgH1iS03: C, 5 7 . i 3 ; H, 9.15; X, i.48. Found: C, 58.35; H , 9.21; N, 6.95. 4-Ethyl-2-methyl-2-0xazoline.~~-As mentioned above this substance was formed when mixtures of 2-amino-1-butanol and acetic acid were heated above 205'. I n a separate experiment N[( 1-hydroxymethyl)propyl]acetamide (65 g., 0.5 mole, prepared above) was heated to 230". Crude oxazoline, b.p. 100-160", escaped when t,he temperature exceeded 205". The crude product was dried and redistilled to give 25 g. (44%), b.p. 73-76' (155 mm.), n Z 5 D 1.4315. Anal. Calcd. for C6Hl1NO: C, 63.68: H, 9.80: X, 12.38. Found: C,63.85; H, 10.00; N, 12.36. 2,4,4-Trimethyl-2-0xazoline.~~-Equimolar amounts of 2amino-2-methyl-1-propanol and glacial acetic acid were heated gradually to 165-170' while volatile material, b.p. 10-130", amounting to 80% of the reactants charged, escaped during 4 hr. The crude distillate was redistilled and an azeotrope of oxazoline and water was collected a t 93-105". This was dried over solid KOH and redistilled to give the pure oxazoline, b.p. 112-113", n Z 5 D 1.4195. .4nal. Calcd. for C ~ H I I S O :C, 63.68: H, 9.SO; K, 12.38. Found: C, 63.31: H, 9 . i 2 ; N, 12.25. 2-Methyl-2-thiazolines (Table II).-The general procedure developed by us is illustrated by the synthesis of 2-methyl-4isopropyl-2-thiazoline (16). The reaction was carried out in B 500-ml. flask equipped with a stirrer, thermometer, simple still head, and condenser. To 60 ml. of mineral oil was added 28 g. (0.193 mole) of K-24 l-hydroxy-3-methylbutyl)acetamide, followed by 25.7 g. (0.116 mole, 50% excess) of Pz&. The mixture was st,irred until well mixed and then was heated gradually to 130" during 1 hr. A vigorous evolution of gas occurred at 90105' and the reaction mixture was held at 110" until this subsided. The reaction mixture was cooled to 80" and 40 nil. of water was added to prevent the mixture from solidifying. About 100 ml. of 20% aqueous S a O H was added to bring the reaction mixture to pH 10 or higher, and the mixture Tvas then steam distilled until collection of the thiazoline became quite slow. The crude thiazoline was extracted from the distillate by ether, the extract was dried (KOH), and the product was recovered by distillation under the conditions stated in Table 11. When the mineral oil was omitted aud the flask was heated by a free flame, the exothermic reaction that occurred was usually too difficult to control. I n large-scale runs the reaction was controlled by withholding much of the P& until the reaction n-as proceeding smoothly at 100-110" and then adding the balance in portions.6 I n these large runs a 20% excess of the pentasulfide was adequate. I t was convenient to separate the bulk of the mineral oil layer by decantation and pour the black tarry product layer directly into cold 20% aqueous YaOH, in which it dissolved, then to carry out the steam distillation. The higher molecular weight thiazolines 17 and 18 steam distilled slowly and so were conveniently removed from the alkaline solution by extraction with ether. When mineral oil was present after the reaction mixture was made strongly basic, some thiazoline escaped into it: this was easily renoved from the mineral oil solution by extraction with cold dilute HCl. The thiazolines are all unpleasant smelling, colorless, waterinsoluble, mobile liquids, whose boiling points and refractive (29) Mentioned b u t not described by P. (lY45j.
r
Tryon,
U. 9 . P a t e n t
2,3iZ,40Y
