The Metabolic Fate of Some Silicon-Containing Carbamates'
:\fter iicyestioii, I ) i h ( l i j ~ ( l n itx~~ ~ ~ ~ ~ l i y l ~ ~ l i i i i c ~ d ilv~x~r hl isi i al :t ~ t (111 c t ~ j , [ t ~ y i l t ~ i ~ x yhi i~i L t ~~~t l i i i i e ~ l ~ y l - ~ ~ - p l o ~ ~ y I aibiie c a h a m a t e ( I\'), a i d l ~ i ~ ( l i ~ t i i ~ o ~ ~ r ~ ~ e ~ l i ~ l ) i ~ i e t l i ~ l - nclicd):i.riia(e - p r o p ) - l s i l(si1:~riieprol):iniate) alle ( \ ~ :iw ) absorbed and eliniiiiated iii the iiririe of ra 111 is eliminated lulchaiiyed. I is metabolized; bis(hydroxymethy1)tetramethyldisiloxaiie dicarbamate -1) WLS isolated from the iirine. \. is also met>abolized; two prodi i c t s isolated from the iirine were a disiloxaiie \.I1 as the mitior compoiietit a t i d bis(hydroxymethyl)(2-hydrox?-propy1)methylsilane dicarbamate (TIII) as t,he major compoiieiit. The data iiiditxtlr that dealkylation is oite of the metabolic paths for elimiiiatioii of orgaiioeilic>oiicompolliids. t b
Although organosilicon coiiipouiids are u d both i i i rommerce aiid in medicine, little is Biiown about their metabolic fate. Pan1 and Povcr' have provicled cvideiice that methyl w-(trimethj 1silyl)dodecoiiate and t riiiiethylsilylhexaclecane are absorbed from the gastiuiiitcstiiial tract of rats. Dow Coriiing4 has reported that [14C']niethylpolysiloxarieis iiot excreted n s 1 4 C 0 2 . Our o\ui interest in the niet:tbolisni of orgaiiosilic*oii c~mipouiidswas stimulated by the 1:wll of oral :wtivity of silanieprobamate (V), although it sho~vedthe bailie EDjo (rotating rod) as nicprobaniatc (I) whcn it ~\-;i< tlosed iritr:~peritoiieally.i It \\ :ih felt t1i:rt this diflcrei1c.c in activity could be clue either t o ;i l:w1\ of nbsorptioii of the silicon coinpound wheu dosed orallj or t o :I different detoxificatioii path11 a\ . The metabolisni of I itself hns been btudied by :L number of investigators.'j Oxidation of the propyl group provides the major puthrvay of detoxification. Cnrboxymeprobainate, l;etcimeprobainate, and hj.tlloxymeprobamate (11) have beeii identified as metabolites (see Scheme I). Thc relative amouiits of these riictabolites vary with t he spc&s; lion ever, thti alcohol I1 is the major detoxification prod\ic.t.
methl 1)dinwthjl-~i-~~ro~)ylsilniie rnrbamate (II?),: [ l i d ila me p ro b arriatt (T T ) .
5
1
(
ll,>t((ql
I , ) l ( ' f I ~ O ( Y ) XI.I Ill )I-(
).
/ ~ - ~ ~ , l l ~I-(~)('(t ,s ( ~I 1 l ~ ~ ) ~ ~ ~ l I
I\
' I I T ~ f I('1 I j )i( ' I I A )('( ) N I I \
)I
111 our prcvious ~ ) r l < we, ~were :tble to slion that 111 showed iio I,harIiiucological activity (rotating rod test) at iiitraperitonezd close levels up to 300 nig, kg. 111 the present Ytucl), .v\-I-ieri I11 orally dosed in rats, material \vas isolated from the line unaltered conipou~id. So acrvecl for this particu1:ir coiiipouud. Compountl I\' \iloTred 111 I!mj" of 15s (14s-169) nig/ kg ip.; -\ftc>roral dosing ~ iIV ' in rats, :hoiit 90", of the ingested SiliCOli could be detected iri the uriiit' mithiii Idais. 111the ethyl ether extract of the ririiie, iio uric~harigetiI\' could be detecwd. l:rum :in ethyl acetate extraction, there I\ a s obtained a silicwiicvntaiiiirig o i l , whieh wab >uhjected to chroni~~tographic. srparatioii. white crystalline solid, nip 66 YOo, !\as isolatetl. The iimr spectrum of this materid 3 c HL\IL I showed t w sharp siiiglets aiid a broad band, which, ( - 1 I {('I I?( '1 12c((7r 4 )(C€I,OCONlI. J from the cheniicd shifts arid areas under these bands, 1 suggested that the solid ir the disiloxarie 1'1. ?'hc r,cI Iofjcirc(ciiJi ( ('I )CC)SI infrared spectrum and the elemental analysis of this 11 iiiuterial are in agreement with this structure assign( ird( v fTAc i (w3I ( ('1 i2()CY I N i I? ): + nieiit. This metabolite a C ~ O L l I i t 5for 29% of the silicoii tI02('('I€2('11LC~CH~)~CI-I,oC'O?;I of the ingested rilacarbamatca IV. KO other silicoli nietabolites u-cr(2 det This study is coricerried with the ideritificatioii ~ i ' the metabolites appearing in the uriiie arising from the H C CH, oral dosing of some silacarbamates, bis(hydroxyI I IV NH-COOCH2SiOSiCH20CONHmethyl) dimet h ylsilane dicarbamat e (111), (hydrox j +
-
(11
~7
-
(1) Tllis revearcli mas supported
11) l'iiblic IIealtli Research Grant C:AI13914 from the Kational Institiire of Genmal Medical Sciences. (2) Alfred P. Sloan Fellon-, 1963-198i. ( 8 ) J. Paul and I T . E'. R. Pover, d r c l i . Btochenz. B i o p h y s . , 87, 312 (19601. (4) A s reported in "The Bulletin," Vol. 11, No. 4, Don. Corning Cenzer for Aid to Medical Research, Midland, Mich., April 1960, p 1.5. ( 5 ) R. J. Fessenden and Marvin D . Coon, J . M e d . Chem., 8 , 604 (1963). ( 6 ) (a) 13. J. Ludwig, J. F. Douglas, L. R. Powell. AI. Meyer, and E'. A I . ed. Pharm. Chem., 3, .53 (1461); (b) F. A I . Berper. .I. P/iarnwr.n/. E r p t l . Thrrup., 112, 413 (1954); ( v ) 13. \ \ . :Agranoff, H . \ I . 13r:liIlev, a1111 .I. A x e l r d , P ~ o cS. O C . 12rptL H t o l . M d . ,9 6 , L'ri I 1CLp>7).
I I
HjC CHj
VI
&Afteroral dosing of silameprobamate, 80-90cz ot the ingested silicon was found in the urine withiii :i days. Extractiori aiid chromatographic separation afforded a solid material (mp 34-58') and :I viscous oil. T*nfortunately, iirither of these substaiiccs roulti be ubtairirtl in :LLI a i i a l y t i c a l l y pure forrii.
On the basis of spectral evidence, the solid can be tentatively assigned the structure of the disiloxane VII. ?he chemical shifts in the nmr spectrum of this material are almost identical with those of the nmr of the disiloxane VI, except that the ratio of the area under the upfield singlet to that under the downfield singlet was 6: 8, rather than 4 : 11, as observed for VI. The infrared spectruni showed absorption chamcteristic3r of the CC ) S R g , SiCH,, and SiOSi functions.'
CHa(NH&02CHz),SiOH, in the case of VI, which xould be mater soluble and which would readily condenselo to the observed disiloxanes under the conditions employed for isolation. t
I
CHJCHCH,Si-
I
+
H,O
H,C CHI
i'
I I
+
(NII ~OOCH~),SiOSi(CH?OCONTT,)
VI1 (minor) CH ,CHOHCHLSi(CH,)(CH?OCONH~)~ VI11 (major)
A combination of chemical and spectral evidence was used to assign tentatively the structure of the hydroxysilameprobamate VI11 t o the oil. The oil is soluble in water, gives positive iodoform and ceric nitrate tests, and contains 10.5% silicon. Structure VI11 should contain ll.2yOsilicon arid should also give positive iodoform and ceric nitrate tests. The infrared spectruni of this compound shoJved a broad hand at 2.S-3.1 p , which can be assigned to the combined absorption of the OH and SHS groups. Absorption was also observed at 3.85 and 6.25 (characteristic of the carbamate function), 7.93 (SiCH,), and 9.2 p (C-0). The characteristic SiOSi absorption at 9.3 1.1 was absent. The nmr spectrum of the oil in D20 is summarized in the Experimental Section. There mere observed two singlets (SiCH3 and SiCH20) arid three peaks in the alkyl region (overlapping doublets, CH,CHOHCH,Si). The multiplet for the proton on the hydroxyl carbon (CH3CHOHCH2Si)is partly masked by the singlet of the SiCH2O group but is evident slightly upfield from the singlet. The relative areas under these three groups of bands are in the ratio of 3.0:5.2:5.0. The acidic protons can be expected to exchange with D20 and, indeed, a strong peak at 8 4.65 (water) was evident. From these data, it can be concluded that dealkylation, as well as oxidation, is one of the metabolic pathways for organosilicon compounds. It should be pointed out that the loss of an alkyl group from an organosilicon compound is not an unexpected observation. Oxidative hydroxylation at the W-1carbon atom of alkyl groups is well known.* With a propylsilane, such oxidation would occur fl to the silicon. It can be expected that, during the course of the metabolic oxidation, an electron-deficient center (illustrated as a carbonium ion below) would be generated. In the laboratory, the formation of an electron-deficient center 0 to a silicon atom can result in d e a l k y l a t i ~ n . ~Although evidence is lacking, it is probable that the dealkylated metabolites were actually silanols [e.g., (7) The infrared absorption of the disiloxane group is in the 9 5-p region a n d is \cry broad and intense Absorption for C-0 1s generall) obseried in the 9 2-p region, b u t is sharper and less intense I n this case, both bands were observed in the spectrum (8) (a) R T Williams, "Detoxication Mechanisms " 2nd ed, John Wiley a n d Sons, Inc , Nen York, K Y , 1959, p 693 ff, (b) E. I T . .\la> nert and H. B TanDyke, Pharmacal Re5 , 1, 21i (1949). (6) For a summarq of @-elimination reactions see C Eaborn, "Organosilicon Compounds," -4cademic Press Inc , N e a Uorh, N Y , 1960, and V. Bazant. V. C h v a l o a k j , a n d J Kathousky Organosilicon Compounds P a r t I ' Academic Press Inc Neil York, h- T , 1965
CHCH=CH?
4-
I
-Si-OH
I
t
H+
I n summary, it has been shown that the carbamates 111-V are absorbed from the gastrointestinal tract of rats and that IV and V are metabolized. For IV, only the dialkylated metabolite VI was found in the urine. The detoxication path of silameprobamate (V), involving u-1 oxidation of the propyl group, appears to be similar to that for meprobamate (I). The major isolated metabolite for 1' was the hydroxy compound VIII, which is analogous to the major metabolite from I.
Experimental Section'' The preparation of the carbamates 111-V has been described in a previous paper.j Dosing and Urine Collection.-Female rats (Long-Evans), 250-300 g, were starved overnight, then individually orally dosed with the desired compound. The animals were housed separately iii metabolism cages constructed to allow separate collectiori of urine and fecal material. Food and water were given, ad libitum, immediately after dosing. The urine was pooled arid stored under toluene. Silicoii-containing materials were iiot observed in the toluene layer. The fecal material was not investigated. Silicon Analysis.-The pooled urine was filtered through Celite. The volume was measured, a 25-m1 aliquot was transferred to a P t crucible, and 25 ml of concentrated H,SOI was added carefully. The mixture was digested 20-30 min on a hot plate. In some cases, a few drops of fuming nitric acid was added to aid the oxidation. The excess acid was fumed off using an open flame, with care being taken that the liquid did not splatter. The crucible was then flamed to red heat, cooled, and weighed. h few drops of HF was added. The crucible was again t,aken to dryness and flamed, cooled, and reweighed. The difference between the t x o weights was taken as the amount of SiO, present. All arialyses were run in triplicate, and the results are reported as the extrapolated value to the total voliime. Normal rat urine contains an average of 6 mg of Si02/%5ml as determined by t'his method. The weight of the Si02 obtained from the urine of the dosed animals was corrected by this valiie. ITnfortunately, elimination of Si02 by a iiormal rat is extremely variable (0-16 mg/25 ml); therefore, the correction can o111y be an approximation. Thin Layer Chromatographic Analysis.-Development of the plates was carried out using toluene-methanol ( 2 :l ) , and visualization of the plates was generally accomplished using 1 iodine in methanol. Visualizatioii of the carbamates, however, was effected by warming the plates in an oven a t 90" and the11 (10) T h e ease of condensation of silanols to disiloxanes depends upon the hindrance around the Si atom. For example, trimethylsilanol is very difficult t o isolate and condenses very readily t o hexamethyldisiloxane. Triethylsilanol can be distilled b u t is readily converted to hexaethyldisiloxane under dehydrating conditions. See ref 9 for general reviews of this area. ( I 1) Melting points are corrected and were determined on a Fisher-Johns melting point apparatus. C, H, and N analyses were performed by t h e lierkeley Microanalytical Laboratory and Si analyses in this laboratory. Infrared spectra were obtained using a Beckman IR-6 spectrophotometer. The nmr spectra were obtained using a Varian A-60 spectrometer. Values are reported downfield from T h l S in S (ppm) with CHCh or H.0 a s a n internal standard.
