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Biomedical subjects

G Zon

Publications and source records attributed to G Zon.

At least 145 records · Page 8Linked to original sources
PubMed1984

NMR spectroscopic studies of intermediary metabolites of cyclophosphamide. A comprehensive kinetic analysis of the interconversion of cis- and trans-4-hydroxycyclophosphamide with aldophosphamide and the concomitant partitioning of aldophosphamide between irreversible fragmentation and reversible conjugation pathways.

Multinuclear (31P, 13C, 2H, and 1H) Fourier-transform NMR spectroscopy, with and without isotopically enriched materials, was used to identify and quantify, as a function of time, the following intermediary (short-lived) metabolites of the anticancer prodrug cyclophosphamide (1, Scheme I): cis-4-hydroxycyclophosphamide (cis-2), its trans isomer (trans-2), aldophosphamide (3), and its aldehyde-hydrate (5). Under a standard set of reaction conditions (1 M 2,6-dimethylpyridine buffer, pH 7.4, 37 degrees C), the stereospecific deoxygenation of synthetic cis-4-hydroperoxycyclophosphamide (cis-12, 20 mM) with 4 equiv of sodium thiosulfate (Na2S2O3) afforded, after approximately 20 min, a "pseudoequilibrium" distribution of cis-2, 3, 5, and trans-2, i.e., the relative proportions of these reactants (57:4:9:30, respectively) remained constant during their continual disappearance. NMR absorption signals indicative of "iminophosphamide" (8) and enol 6 were not detected (less than 0.5-1% of the synthetic metabolite mixture). A computerized least-squares fitting procedure was applied to the individual 31P NMR derived time courses for conversion of cis-2, 3 plus 5 (i.e., "3"), and trans-2 into acrolein and phosphoramide mustard (4), the latter of which gave an expected array of thiosulfate S-alkylation products (e.g., 16) and other phosphorus-containing materials derived from secondary decomposition reactions. This kinetic analysis gave the individual forward and reverse rate constants for the apparent tautomerization processes, viz., cis-2 in equilibrium "3" in equilibrium trans-2, as well as the rate constant (k3) for the irreversible fragmentation of 3. The values of k3 at pH 6.3, 7.4, and 7.8 were equal to 0.030 +/- 0.004, 0.090 +/- 0.008, and 0.169 +/- 0.006 min-1, respectively. Replacement of the HC(O)CH2 moiety n 3 with HC(O)CD2 led to a primary kinetic isotope effect (kH/kD = 5.6 +/- 0.4) for k3. The apparent half-lives (tau 1/2) for cis-2, "3", and trans-2 under the standard reaction conditions, at "pseudoequilibrium" (constant ratio of cis-2/"3"/trans-2), were each equal to approximately 38 min, which is considerably shorter than the widely cited colorimetrically derived half-lives reported by earlier investigators. The values of tau 1/2 for cis-2, "3", and trans-2 were affected by pH in the same manner as that found for k3 but were relatively insensitive to the presence of either K+, Na+, Ca2+, or Mg2+. The presence of certain primary amines led to marked decreases in tau 1/2 and, in some cases, the formation of acyclic adducts of aldehyde 3.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

31P- and 13C-n.m.r.-spectral and chemical characterization of the end-group and repeating-unit components of oligosaccharides derived by acid hydrolysis of Haemophilus influenzae type b capsular polysaccharide.

Haemophilus influenzae type b capsular polysaccharide [repeating unit, leads to 3)-beta-D-Ribf-(1 leads to 1)-D-Ribol-5-(PO2H leads to] was partially hydrolyzed with HCl to give oligosaccharides that were isolated by size-exclusion chromatography, and then characterized by 31P- and 13C-n.m.r.-spectral and chemical methods, in order to determine the end-group composition and, hence, the number-average chain-length (L). The ratio (approximately 17:8) of monophosphate end-groups to D-ribofuranose end-groups revealed the relative rates of hydrolysis of the phosphoric diester linkage and the glycosidic linkage in the repeating-unit structure. Cleavage of the phosphoric diester linkage was approximately 92% regioselective, as indicated by the approximately 12:1 ratio of D-ribofuranose monophosphate end-groups to D-ribitol monophosphate end-groups. The n.m.r. spectra of the oligosaccharide repeating-unit provided evidence for partial stereomutation (approximately 3-8%) that involved rearrangement of the D-ribofuranose phosphoric diester linkage and anomerization at C-1 of D-ribofuranose. Variously sized oligosaccharides (L = 4, 7, and 12), that had D-ribofuranose end-groups reacted with bovine serum albumin that had an average of approximately 9 adipyl hydrazide functionalities, to give, within experimental error, quantitative yields of the corresponding hydrazone-linked, oligosaccharide-protein conjugates.

Carbohydrate Conformation↗
PubMed1983

Synthesis and evaluation of 3-halocyclophosphamides and analogous compounds as novel anticancer "pro-prodrugs".

3-Fluoro-, 3-chloro-, and 3-bromocyclophosphamide were prepared from the reaction of trifluoromethylhypofluorite, sodium hypochlorite, and bromine with the anticancer drug cyclophosphamide. Treatment of cis- and trans-4-phenylcyclophosphamide and 5,6-benzocyclophosphamide with sodium hypochlorite afforded cis- and trans-3-chloro-4-phenylcyclophosphamide and 3-chloro-5,6-benzocyclophosphamide, respectively. 31P-NMR spectroscopy was used to study the reactivity of these compounds: the fluoro derivative was reduced to cyclophosphamide on incubation with mouse liver slices, and the reactivity order for sulfhydryl-induced reduction of the 3-halocyclophosphamides was Br approximately equal to Cl much greater than F. Compared with the therapeutic efficacy of cyclophosphamide against L-1210 and P-388 cancers in mice, 3-fluoro- and 3-chlorocyclophosphamide were less active, although the fluoro derivative was more efficacious than the 3-chloro compound. The individual R and S enantiomers of 3-chlorocyclophosphamide, prepared from (S)- and (R)-cyclophosphamide, respectively, showed no significant difference in therapeutic activity in the P-388 test system.

Animals↗
PubMed1983

O-imino esters of N,N-bis(2-chloroethyl)phosphorodiamidic acid. Synthesis, X-ray structure determination, and anticancer evaluation.

Nine representatives of the title series of compounds [(ClCH2CH2)2NP(O)(NH2)ON = CRR'] were synthesized as potential anticancer prodrugs, based on the possibility of enzymatic reduction of the N-O bond to release the known cytotoxic agent phosphoramide mustard [1, (ClCH2CH2)2NP(O)(NH2)OH]. The dimethyl derivative (2, R = R' = CH3) exhibited a statistically significant, albeit low, level of anti-L1210 activity in mice. Derivative 2, which was shown by 31P NMR measurements to be very stable toward hydrolysis at 37 degrees C over a pH range of 5.7-7.4 (T1/2 congruent to 7-8 weeks), gave colorimetrically detectable amounts of alkylating material upon incubation with mouse liver slices: approximately 3-5% conversion after 20 min at 37 degrees C. A single-crystal X-ray study of 2 revealed an unusual hydrogen-bonded "ladder" and a very similar steric relationship for the NCH2CH2Cl and ON = CCH3 moieties.

Animals↗
PubMed1982

O-Methylhydroxylamine as a new trapping reagent for quantitative studies of 4-hydroxycyclophosphamide and aldophosphamide.

31P- and 1H-NMR spectroscopy were used to demonstrate that the primary metabolites of the anticancer drug cyclophosphamide (4-hydroxycyclophosphamide and its acyclic tautomer, aldophosphamide) are quantitatively converted by O-methylhydroxylamine, at pH 7.4 and 37 degrees, into the E and Z isomers of aldophosphamide O-methyl oxime. These trapping products are readily extracted from aqueous media with either chloroform or ethyl acetate, are stable at pH 6-8 toward oxime hydrolysis and elimination of phosphoramide mustard (a secondary metabolite of cyclophosphamide), and showed no evidence for transoximination with either ketone or aldehyde acceptors. All of these features support the use of aldophosphamide O-methyl oxime in quantitative studies related to cyclophosphamide metabolism.

Cyclophosphamide↗
PubMed1982

Synthesis, hydrolytic reactivity, and anticancer evaluation of N- and O-triorganosilylated compounds as new types of potential prodrugs.

N- and O-Triorganosilylated compounds related to various anticancer agents were synthesized for evaluation as potential anticancer prodrugs. 1H-NMR and UV kinetic measurements of hydrolytic desilylation were used to correlate relative rates of structural unmasking with steric bulk about the silicon reaction center. The tert-butyldimethylsilyl ester of chlorambucil and a number of O- triorganosilylated carbamate derivatives of nor-nitrogen mustard showed significant activity against P-388 lymphocytic leukemia in mice.

Animals↗
PubMed1982

Synthesis and study of a spin-labeled cyclophosphamide analogue, 3-(1-oxy-2,2,6,6-tetramethyl-4-piperidinyl)cyclophosphamide.

3-(1-Oxy-2,2,6,6-tetramethyl-4-piperidinyl)cyclophosphamide (7) was isolated in 36% yield following H2O2-Na2WO4 oxidation of 3-(2,2,6,6-tetramethyl-4-piperidinyl)cyclophosphamide (6), which was synthesized in three steps (25% yield) starting with 4-amino-2,2,6,6-tetramethylpiperidine. Binding of 7 to mouse liver microsomes was investigated by optical and electron spin resonance spectroscopy. Compared with the mouse liver microsomal metabolism of 1, separate incubations of 6 and an ca. 1:1 mixture of 1 and 6 gave approximately 90 and 60% less acrolein, respectively. A spin-labeled metabolite of 7, viz., N-(1-oxy-2,2,6,6-tetramethyl-4-piperidinyl)phosphoramide mustard (9), was synthesized and its intramolecular O-alkylation at pH 7.4, 37 degrees C, was studied by 31P NMR spectroscopy. Compounds 7 and 9 were inactive in screening tests against L1210 lymphoid leukemia in mice.

Acrolein↗
PubMed1982

Hydrolytic stability of pneumococcal group 6 (type 6A and 6B) capsular polysaccharides.

The hydrolyses of the immunologically cross-reactive and constitutionally isomeric group 6 pneumococcal polysaccharides, types 6A and 6B, were investigated by 31P nuclear magnetic resonance spectroscopy, gel filtration through Sepharose 4B, reducing-sugar analysis, and rocket immunoelectrophoresis. Phosphorus nuclear magnetic resonance spectroscopy showed that cleavage of the repeating-unit phosphodiester linkages at pH 10, 60 degrees C was considerably faster (greater than 10(3) ) for the type 6A than the type 6B polysaccharide. Under these reaction conditions, 31P nuclear magnetic resonance kinetic measurements showed that the Na+ form of the type 6A polysaccharide underwent phosphodiester-linkage hydrolysis two times slower than the corresponding Ca+2 form; a stoichiometrically excess amount of Ca+2 caused a 30-fold enhancement of the latter hydrolysis rate. The spectroscopic characterization of phosphorus-containing end groups resulting from hydrolysis of the type 6A polymer provided additional mechanistic information. Heating the type 6A and 6B polysaccharides at 56 degrees C for various times led to gel filtration coefficients of distribution (Kd values) which indicated that the type 6A material underwent size reductions considerably faster than did the type 6B antigen; these increased Kd values qualitatively correlated with the loss of immunochemical reactivity measured by rocket immunoelectrophoresis. The application of a statistical theory to the depolymerization of the type 6A and 6B polysaccharides was consistent with random bond cleavage, as evidenced by the calculated versus measured gel filtration patterns. Although the molecular changes causing the size reductions were not fully elaborated, it was established that the acetal linkages of the type 6A and 6B polysaccharides were comparatively resistant to hydrolysis and that depolymerization by hydrolysis of the phosphodiester linkage was a major factor only in the type 6A structure. It was concluded that the hydrolytic stability of the type 6B antigen would favor its use in the polyvalent pneumococcal vaccine rather than the cross-reactive, but comparatively unstable, type 6A polysaccharide, if all other factors are equal.

Chemical Phenomena↗
PubMed1981

Synthesis of 3-hydroxycyclophosphamide and studies related to its possible role in the metabolism of cyclophosphamide.

Hydrogenolysis of 3-(benzyloxy)cyclophosphamide (10) using Pd/C catalyst and ethyl acetate as solvent leads to the formation of 3-hydroxycyclophosphamide (3, approximately 20%) and cyclophosphamide (1, approximately 10%), accompanied by regioselective hydrogen-exchange reactions at the C-4 and C-5 positions in 3 and 1. A variety of oxidizing reagents and liver microsomal incubation failed to provide evidence (31P NMR) for conversion of 1 into 3, whereas identical incubation of 3 led to its reduction to 1. Compound 3 is stable at pH 6.5-8.2, 37 degrees C, and exhibits anticancer activity comparable to 1 when tested against L1210 leukemia in mice. Data are discussed with regard to a previously reported suggestion that metabolism of 1 may involved oxidation to give 3 followed by rearrangement of 3 to 2.

Animals↗
PubMed1980

Synthesis and antitumor activity of cyclophosphamide analogues. 3. Preparation, molecular structure determination and anticancer screening of racemic cis- and trans-4-phenylcyclophosphamide.

Cyclization of racemic 3-amino-3-phenyl-1-propranol with bis(2-chloroethyl)phosphoramidic dichloride gave a diastereomeric mixture of 4-phenylcyclophosphamide (3), which was chromatographically separated into the faster and slower eluting components. A combination of 1H/31PNMR and IR spectral data indicated that the faster and slower racemates correspond to cis-3 (mp 129-130 degrees C) and trans-3 (mp 112-114.5 degrees C), respectively. The molecular structure of the former compound was determined by X-ray crystallography and thereby unambiguously established the cis relationship between equatorially disposed phenyl and P = O substituents in a chair conformation. These results confirm the stereochemical assignments for cis- and trans-3 which have been independently deduced by Y. E. Shih, J. S. Wang, and C. T. Chen [Heterocycles, 9, 1277 (1978)]. Anticancer screening tests against L1210 lymphoid leukemia in mice have revealed that, while both diastereomers of 3 afford toxic metabolites, trans-3 led to therapeutic activity and cis-3 did not. The relevance of these findings to results reported for 4-methylcyclophosphamide and cyclophosphamide is briefly discussed.

Animals↗
PubMed1979

Synthesis, base-catalyzed hydrolytic reactivity, and anticancer evaluation of O-aryl phosphorodiamidates as a novel class of pro(phosphorodiamidic acid mustards).

Bis(2-chloroethyl)phosphoramidic dichloride [MP(O)Cl2, M = N(CH2CH2Cl)2] has been used as the starting material for the synthesis of O-aryl phosphorodiamidates having the general structure MP(O)(NHR)OAr: 9, R = H, Ar = 4-NO2C6H4; 10, R = H, Ar = C6F5; 11, R = C6H5, Ar = C6F5; 12, R = 4-MeC6H4, Ar = C6F5; and 13, R = 4-EtOC6H4, Ar = C6F5. The phosphorodiamidic chloride precursor to 13 (14) was also isolated. Kinetics for the base-catalyzed hydrolysis of compounds 9--13 were investigated by UV and NMR methods and are considered in connection with service of these compounds as pro(phosphorodiamidic acid mustards) [MP(O)(NHR)OAr leads to MP(O)(NHR)OH] via an E1cB mechanism involving the intermediacy of a mustard-bearing metaphosphorodiimide [MP(O)=NR]. Anticancer screening tests against L1210 lymphoid leukemia in mice indicated that 9--14 are inactive; similar negative results were obtained with the KB cell culture, except in the case of 14 which was marginally active.

Animals↗