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PubMed1981

Irreparable DNA cross-links and mammalian cell lethality with bifunctional alkylating agents.

The appearance and removal of DNA cross-links in C3H10T1/2 cells has been investigated with closely related bifunctional alkylating agents having widely different kinetics of alkylating activity. Concentrations of nitrogen mustard, phosphoramide mustard and melphalan demonstrating equivalent levels of cell lethality indicate a correlation between the appearance of residual DNA cross-links, transformation and the loss of colony formation ability. Residual DNA cross-links appear to remain after repair is nearly complete by 24 h and consist of both the interstrand DNA and DNA-protein varieties. These adducts occur in the general population of cells despite the fact that these cells retain their DNA cross-link repair capabilities. Less than 100 interstrand DNA cross-links and a 10-fold greater number of DNA-protein cross-links are estimated to remain in the DNA after a 66% lethal dose of these compounds. Due to the obvious complications involving DNA replication in the presence of such lesions, residual DNA cross-links may possibly be associated with lethality in these cells. Current evidence demonstrating the formation of additional sites of alkylation such as irreparable phosphotriester adducts by several alkylating agents may suggest a role for a specific type of DNA damage in this process.

Alkylating Agents↗
PubMedDate not supplied

DNA alkylation by mustard gas in yeast strains of different repair capacity.

Reaction of the toxic and mutagenic alkylating agent mustard gas with DNA of the yeast Saccharomyces cerevisiae was analyzed qualitatively and quantitatively. Within the dose range tested (2 X 10(-5)-2 X 10(-3) M) DNA in vivo is alkylated dose-proportionally. DNA alkylation and relative distribution of purine derivatives are not influenced by the cell's sensitivity towards the mutagen. At LD37 (4.4 X 10(-4) M) the wild type contains 44 300 purine derivatives: 9200 3-alkyladenines (20%), 29600 7-alkylguanines (67%) and 5500 diguaninyl derivates (13%) per genome. In sensitive strains the number of derivates per genome at LD37 is reduced according to the dose reduction factor. Alkylation at the position O6 of guanine by mustard gas cannot be shown, the method's limit of detection being 0.3% amongst purine derivates.

Alkylation↗
PubMed1995

Comparison of the sequence selectivity of the DNA-alkylating pluramycin antitumour antibiotics DC92-B and hedamycin.

The sequence selectivity of DNA alkylation by the recently isolated pluramycin antitumour antibiotic DC92-B has been investigated using two methods: a piperidine-induced strand-breaking procedure and a Taq DNA polymerase/linear amplification method. These techniques reveal that guanines are the most reactive sites for alkylation and that the level of adduct formation at these sites is clearly sequence dependent. The highest levels of alkylation occurred at isolated guanines located in 5'-CGT sequences and also at the 5'-G in some 5'-CGG sequences. Isolated guanines in 5'-TGT sequences were also quite reactive. We have also re-examined, in parallel, the sequence selectivity of binding of the structurally-related compound hedamycin: the first known example of a bis(epoxide)-containing, DNA-alkylating pluramycin. Our studies included a more extensive sequence analysis of hedamycin binding than that previously reported and we are able, therefore, to define more precisely the sequence preference. Despite significant differences in the stereochemistry and substitution of their bis(epoxide) sidechains, hedamycin and DC92-B exhibited very similar sequence selectivities in our assays.

Alkylation↗
PubMed1995

The influence of 4-alkyl substituents on the formation and reactivity of 2-methoxy-quinone methides: evidence that extended pi-conjugation dramatically stabilizes the quinone methide formed from eugenol.

The effects of para-alkyl substituents on both the cytochrome P450-catalyzed oxidation of phenols to quinone methides (QMs; 4-methylene-2,5-cyclohexadien-1-ones), and on the rates of nucleophilic additions to the QMs were investigated. The derivatives of 4-alkyl-2-methoxyphenol studied were 4-methyl (creosol), 4-ethyl, 4-propyl, 4-isopropyl, and 4-allyl (eugenol). The relative reactivities of QMs derived from these phenols with water were 4-methyl > 4-ethyl = 4-propyl > 4-isopropyl > 4-allyl. These variations in rate were rationalized by differences in stabilization of positive charge density at the site of nucleophilic attack. In particular, saturation of the vinyl substituent on eugenol-QM increases the solvolysis rate 100-fold. This effect is presumably due to the loss of the contribution of an additional aromatic resonance structure to the overall resonance hybrid of the QM from 2-methoxy-4-propylphenol. Finally, the kinetic results show that there is a 472-fold difference in reactivity within this series of QMs. The QM glutathione conjugates were synthesized and characterized by 1H-NMR and electrospray mass spectrometry and a HPLC assay was developed to quantify QM formation in rat liver microsomes. The general trend is increasing alkyl substitution at the para position results in more QM; however, in contrast to the large range of reactivities of the QMs observed in the kinetic experiments, the amounts of P450-derived QM GSH adducts varied only by a factor of 3. In particular, similar amounts of the QMs from eugenol and 2-methoxy-4-propylphenol were produced which suggests that the lack of reported hepatotoxicity for the latter phenol in mice depleted of GSH, may be due to the extreme reactivity of 4-propyl-QM that would be rapidly detoxified by hydrolysis. These data suggest that there may be a threshold cytotoxicity level for QMs related to their reactivity which may affect the relative toxicities of 4-alkyl-2-methoxyphenols.

Alkylation↗
PubMed1995

Alkylating derivative of hexadecamethonium protects muscle synaptic acetylcholinesterase against inhibition.

The action of the alkylating derivative of hexadecamethonium on frog neuromuscular transmission was studied with the help of intracellular microelectrodes. Treatment of frog m. cutaneous pectoris-n. pectoralis preparations with the alkylating derivative of hexadecamethonium (0.5 microM) for 30 min led to an irreversible decrease in the amplitude of the end-plate potentials by 2.5-fold without a change of their latency period or quantal content. Such treatment led also to a considerable reduction of the anticholinesterase effects of neostigmine and of the organophosphorus irreversible inhibitor, armine. Thus, when applied to intact nerve-muscle preparations, neostigmine (2 microM) or armine (1 microM) increased the amplitude of end-plate potentials by 80-90%, and the rise time and half-decay time by about 2- to 3-fold. However, after the nerve-muscle preparations were pretreated with the alkylating derivative of hexadecamethonium (0.5 microM, for 30 min), the amplitude of end-plate potentials increased by 20-25%, rise time by 15-20% and half-decay time by 40-50% only. Investigation of muscle acetylcholinesterase activity, using the Ellman technique, showed that the alkylating derivative of hexadecamethonium diminished the sensitivity of the muscle acetylcholinesterase to inhibition without exerting its own inhibitory action.

Action Potentials↗
PubMed1989

Synthesis of alkylating oligonucleotide derivatives containing cholesterol or phenazinium residues at their 3'-terminus and their interaction with DNA within mammalian cells.

5'-[32P]-labelled alkylating decathymidylate [4-(N-2-chloroethyl)N-methylaminobenzyl]-5'-phosphamide derivatives containing cholesterol or phenazinium residues at their 3'-termini were synthesized and used for alkylation of DNA within mammalian cells. The uptake of the cholesterol derivative by the cells and the extent of DNA alkylation are about two orders of magnitude higher than those of a similar alkylating derivative lacking the groups at the 3'-termini. The presence of the phenazinium residue at the 3'-terminus of the oligonucleotide reagent does not improve the reagent uptake by the cells but drastically increases the DNA modification efficiency.

Alkylating Agents↗
PubMed1995

Conformational stability of Cys45-alkylated and hydrogen peroxide-oxidised glutathione S-transferase.

A highly reactive cysteine residue in class pi glutathione S-transferases enhances their susceptibility to chemical alkylation and oxidative stress. Alkylation of the reactive Cys45 in the porcine class pi enzyme (pGSTP1-1) with either N-iodoacetyl-N'-(5-sulpho-1-naphthyl)ethylenediamine or iodoacetamide results in a loss of enzyme activity and glutathione-binding function. Similarly, oxidation of pGSTP1-1 with hydrogen peroxide (H2O2) also results in a loss of catalytic and glutathione-binding function, but these effects are reversed by the addition of 5 mM glutathione or dithiothreitol. Analysis by SDS-PAGE of the H2O2-oxidised enzyme indicates oxidation-induced formation of disulphide bonds involving Cys45. Equilibrium-unfolding studies with guanidinium chloride indicate that the unfolding of Cys45-alkylated and H2O2-oxidised pGSTP1-1 can be described by a two-state model in which the predominant thermodynamically stable species are the folded dimer and unfolded monomer. Unfolding transition curves suggest that the introduction of a large and bulky AEDANS at Cys45 does not affect the unfolding pathway for pGSTP1-1. H2O2-oxidised pGSTP1-1, on the other hand, appears to follow a different unfolding pathway. This appears not to be a result of the introduction of disulphide bonds since the reduction of these bonds in the oxidised protein with dithiothreitol does not affect the unfolding transition. Furthermore, the conformational stability of the oxidised protein is significantly diminished (delta G(H2O) = 11.6 kcal/mol) when compared with unmodified and AEDANS-alkylated enzyme (delta G(H2O) = 22.5 kcal/mol).

Alkylation↗
PubMed1986

The affinity alkylators, 11 alpha-bromoacetoxyprogesterone and estrone 3-bromoacetate, modify a common histidyl residue in the active site of human placental 17 beta,20 alpha-hydroxysteroid dehydrogenase.

Purified human placental 17 beta,20 alpha-hydroxysteroid dehydrogenase (native enzyme) was completely inactivated by the affinity alkylator, estrone 3-bromoacetate, in the presence of cofactor (NADPH). The inactivated enzyme was reactivated to 100% activity by base-catalyzed hydrolysis of the steroidal ester-enzyme conjugate and then repurified by dialysis. Control enzyme in mixtures which contained estrone in place of alkylator was treated the same as the reactivated enzyme. 11 alpha-Bromo[2'-14C]acetoxyprogesterone, an active site-directed affinity alkylator of the enzyme, produced 5.0-fold less radiolabeled 3-(carboxymethyl)histidine and S-(carboxymethyl)cysteine plus 1.4-fold more 1,3-bis(carboxymethyl)-histidine in the reactivated enzyme than in the control enzyme. The lesser amount of S-(carboxymethyl)cysteine and greater amount of 1,3-bis(carboxymethyl)histidine resulted from nonspecific interactions between the reactivated enzyme and the progestin radioalkylator. The nonradiolabeled 3-(carboxymethyl)histidine originally produced by estrone 3-bromoacetate in the enzyme active site hindered radioalkylation of this amino acid by 11 alpha-bromo[2'-14C]acetoxyprogesterone to yield 5-fold less radiolabeled 3-(carboxymethyl)histidine in the reactivated enzyme relative to control enzyme. Thus, the estrogen and progestin affinity alkylators modified a common histidyl residue in the active site. These studies are direct evidence that the estradiol 17 beta-dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase activities reside at a common locus on a single protein.

Alkylation↗
PubMed1987

Coupling of multiple opioid receptors to GTPase following selective receptor alkylation in brain membranes.

Opioid agonists of the mu, kappa and delta types stimulated low-Km guanosine triphosphatase (GTPase) in membranes, from the brain of the rat by up to 34%, with potencies the rank order of which corresponded to the respective binding affinities to opioid receptor. In general, kappa ligands stimulated GTPase to a lesser degree than mu or delta opiates. The coupling of a given type of opioid receptor to GTPase was resolved by direct or protective alkylation of the other receptors. Treatment of the membranes with beta-funaltrexamine abolished the stimulation of GTPase by sufentanil and levorphanol (mu), but not by bremazocine (kappa) or DSLET (delta). On the other hand, prior incubation with Superfit, an alkylating agent with selectivity for the delta opioid receptor, specifically eliminated the effect of DSLET. Partial alkylation by increasing concentrations of Superfit gradually reduced the extent of stimulation of GTPase by DSLET. The successive treatment of membranes with Superfit and beta-funaltrexamine blocked the actions of DSLET, sufentanil and levorphanol, but had no effect on the stimulation of the GTPase by bremazocine. Selective coupling of an opioid receptor to GTPase was also obtained after incubation of membranes with beta-chlornaltrexamine in the presence of protective concentrations of mu, kappa or delta opioid ligands. Alkylation resolved the coupling of the non-selective opiate etorphine: the sum of stimulation of GTPase in the receptor-selective membranes equalled maximal stimulation of enzyme in untreated membranes. Naloxone blocked the stimulation of GTPase by mu, kappa or delta agonists, but ICI-174,864 specifically inhibited the effect of DSLET.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylation↗
PubMed1995

Further studies on 6-alkylandrost-4-ene-3,17-diones as aromatase inhibitors: elongation of the 6-alkyl chain.

To gain further insight on the relationship between 6-alkylandrost-4-ene-3,17-diones and their aromatase inhibition activity, a series of alkyl steroids with long alkyl chains (n-pentyl, n-hexyl, or n-octyl) at C-6 alpha and 6 beta were synthesized. All of the steroids studied inhibited human placental aromatase in a competitive manner with apparent Ki values ranging from 2.8 to 80 nM. The 6 beta-pentyl analog 4a (Ki = 2.8 nM) was the most potent inhibitor. The inhibitory activities of the 6 beta-alkyl steroids 4 were more powerful than those of the corresponding 6 alpha-isomers 5. The addition of one methylene unit to the 6 alpha- and 6 beta-n-butyl moieties of androst-4-ene-3,17-dione markedly increased the affinity to aromatase, whereas further elongation of the n-pentyl group decreased affinity in relation to the carbon number of the alkyl chain. These results, along with molecular modeling with the PM3 method, suggest that the increased affinities of the pentyl steroids 4a and 5a may essentially depend on the formation of thermodynamically stable enzyme-inhibitor complex in the hydrophobic binding pocket.

Alkylation↗
PubMed1989

Mutagenicity and alkylating activity of the aqueous chlorination products of humic acid and their molecular weight fractions.

Fluka humic acid used as a model substrate in these studies was analysed for elemental and the oxygen-containing functional groups. It was chlorinated at C:Cl molar ratios of 1:1 and 1:0.3 and subsequently separated into molecular weight fractions by ultrafiltration. The freeze-dried, chlorinated humic acid and the respective molecular weight fractions were analyzed for TOC, TOX, alkylating activity using 4-(p-nitrobenzyl)pyridine and mutagenicity by the Ames/Salmonella/microsome assay with strains TA-98 and TA-100. Results indicated that predominantly non-volatile, direct-acting mutagenic and/or alkylating agents were formed during humic acid chlorination and that these agents were unevenly distributed among the various molecular weight fractions. Formation of mutagenic and alkylating agents were highly dependent upon level of chlorination and total organic carbon. Higher levels of mutagenic and alkylating activities were produced with increasing concentration of chlorine in the range of 0.4-1.2 chlorine equivalents per mole of carbon. However, both these activities in the freeze-dried, chlorinated humic acid solutions containing the non-volatiles or the fresh solutions decreased gradually with increasing pH and storage time, apparently due to degradation and hydrolysis of some of the components.

Alkylating Agents↗
PubMed1983

Inhibition of tumor growth by an alkylation of the plasma membrane.

The effect of nitrogen mustard (2-chloro-N-2-chloroethyl-N-methylethanamine), Trenimon (2,3,5-trisethyleneiminobenzoquinone-1,4), chlorambucil (4-[p-(bis[2-chloroethyl]amino)-phenyl]butyric acid) and phosphamide mustard (N,N-bis(2-chloroethyl)-diamidophosphoric acid) on Na+/K+-ATPase, membrane fluidity and cell multiplication was studied. With the exception of chlorambucil which does not affect Na+/K+-ATPase all concentrations of the other alkylating agents which inhibit cell multiplication of Ehrlich ascites tumor cells depress the activity of the Na+/K+-ATPase. All alkylating agents--including chlorambucil--caused an increase in the apparent degree of fluorescence polarization after labelling of the plasma membrane with 1,6-diphenyl-1,3,5-hexatriene (DPH). This effect is interpreted as a decrease in membrane fluidity caused by the alkylating drugs. The decrease in membrane fluidity is due to a direct interaction of the alkylating agent with the plasma membrane and is expressed at all concentrations of the drug which inhibit cell proliferation. No effect on membrane fluidity is observed after treatment of cells resistant to nitrogen mustard. The biological consequence of a decrease in membrane fluidity was investigated by growing Friend erythroleukemia cells in the presence of 10 mM cholesterol hemisuccinate. This procedure raises the microviscosity of the plasma membrane and depresses cell proliferation.

Alkylating Agents↗
PubMed1984

Depression of histone acetylation by alkylating antitumor agents: significance for antitumor activity and possible biological consequences.

Treatment of Ehrlich ascites tumor cells with the alkylating antitumor agents triaziquonum, N-mustard and cyclophosphamide leads to a reduction in the posttranslational incorporation of 3H-acetate into histones and the extent of histone acetylation in Ehrlich ascites tumor cells. All core histones are affected. The depression of histone acetylation is not the result of a decrease in acetyl-CoA. Evidence is presented for an activation of histone deacetylase by alkylating agents. A reduction of histone deacetylation is observed after exposure to all concentrations of alkylating agents which inhibit cell proliferation. In order to evaluate the biological consequences of a reduction of histone acetylation, the extent of acetylation was modulated by either chemical acetylation or treatment with butyrate. In all cases an increase in histone acetylation leads to an enhancement of the rate of transcription. In accord with previous reports from our laboratory (1), it is concluded that the reduction of histone acetylation affects RNA synthesis. It is emphasized, however, that besides a regulation of transcription, histone acetylation may be involved in other cell functions. Thus, the complete biological consequences of the reduction of histone acetylation remain to be elucidated. In view of the antitumor activity of the alkylating agents it seems noteworthy that hepatoma AS30D cells are characterized by a remarkably higher extent of histone H4-acetylation compared to normal, adult, fetal, or regenerating liver.

Alkylation↗
PubMed1985

Plasma membrane as target of alkylating agents.

N mustard resistant Walker cells exhibit the same frequency of DNA interstrand cross-links and the same rate of cross-link removal as the sensitive parental line. Employing cytostatically active concentrations of chlorambucil covalently bound to polyethyleneimine, the extent of DNA cross-linking is reduced to levels observed in the presence of nontoxic concentrations of free chlorambucil. It is concluded, therefore, that DNA cross-links alone are not sufficient to explain the inhibition of cell multiplication by alkylating agents and that additional mechanisms have to be considered. Evidence for an interference of alkylating agents with several enzymes of the plasma membrane is presented. An inhibition by N mustard of the furosemide-sensitive Na+/K+/Cl- -cotransport and the Na+/H+-antiport is described in greater detail. Considering the fact that the enzymes which are affected by alkylating agents are controlled by growth factors it was investigated whether a synergism between inhibitors of early growth-factor-controlled reactions and alkylating agents is to be seen. It is demonstrated that mepacrine, an inhibitor of phospholipase C, and the calmodulin binding drugs, chlorpromazine and flunarizine, amplify the action of N mustard.

Adenosine Triphosphatases↗
PubMed1988

Enzymatic mechanisms of resistance to alkylating agents in tumor cells and normal tissues.

The presence in tumor cells and in normal cells of enzymes which metabolize and inactive alkylating agents appears to play a major role in determining the effectiveness of alkylating agents against human tumors and the toxicities of these agents to normal tissues. The enzyme aldehyde dehydrogenase appears to protect bone marrow and the gastrointestinal tract against toxicity from cyclophosphamide and other closely related oxazophosphorine agents. The presence of this enzyme in bone marrow stem cells facilitates the elimination of tumor cells from bone marrow suspensions, with preservation of the ability of the marrow suspension to reconstitute normal hematopoiesis in a patient. A variety of mouse and human tumors has been shown to be resistant to cyclophosphamide on the basis of an elevated aldehyde dehydrogenase content. The clinical significance of this type of resistance is currently being explored. Increased levels of glutathione-S-transferase have been shown to be associated with cellular resistance to a variety of alkylating agents. We have identified and characterized the conjugates of nitrogen mustards with glutathione. The formation of these conjugates is catalyzed by glutathione-S-transferase. The further study and characterization of these specific reactions should contribute to the understanding and quantitation of this type of alkylating agent resistance.

Aldehyde Dehydrogenase↗
PubMed1994

The alkylating properties of chlorambucil.

Previous work has indicated an aziridinium ion mechanism in the hydrolysis of chlorambucil, and the present work on the alkylation of nucleophiles fully supports this mechanism. This mechanism forms the basis for understanding the kinetics of alkylation reactions because their rates are limited by the rate of formation of the aziridinium ion and the alkylation reaction competes with the hydrolytic reaction. We have measured alpha N, where alpha N(N) is the rate of reaction of the aziridinium ion with a nucleophile N relative to its reaction with water for several nucleophiles that are related to those found in proteins. The alpha values for hydroxide ion and some other bases are greater than 10(3), but the effective values at pH 7.5 are much smaller because there is little base present. The kinetic equations show that it is very difficult to alkylate a nucleophile extensively at pH 7.5 before chlorambucil has hydrolyzed. Therefore, it is not clear why angiotensin-converting enzyme is completely inhibited by low concentrations of chlorambucil. On the other hand, damage to DNA is easily understood.

Alkylating Agents↗
PubMed1984

Effect of reduction and alkylation on structure and function of rabbit IgG antibody--II. Effects on classical pathway C3 convertase formation.

Anaerobic reduction of purified rabbit IgG antibody (Ab) with 1.5 moles of dithiothreitol per mole of Ab at pH 8.0, followed by alkylation, cleaves 39% of the inter-heavy-chain (H-H) disulfide (SS) bonds. This treatment has the following effects on the ability of the Ab to activate the classical pathway of complement. Compared to control Ab, reduced and alkylated (RA) Ab retained 4-5.6% of overall hemolytic activity and 55% of complement-fixing activity at 0 degrees C. Complexes of RA Ab and equivalent amounts of soluble Ag consumed C4, C2 and C3 at 37, 51 and 44%, respectively, of the rate at which these components were consumed by equal concns of complexes containing control Ab. Complexes made with RA Ab bound 18% as much C-1 as those made with native Ab. These data indicate that the principal, if not the only, effect of RA is on C-1 binding. Measurements of the ability of complexes of Ab with cell-bound Ag to bind C-1 showed at most a 20% loss of C-1 binding sites and a ca two-fold decrease in affinity for C-1. Similar results were obtained with purified (activated) C-1 and with native C1 in serum. No significant difference could be detected in the rate of activation of bound C1. Normal rabbit IgG which was reduced and alkylated under the same conditions retained 52% of its H-H SS bonds and 30% of its ability to bind C-1. This finding suggests that the impairment in C-1 binding results from an effect on the C1 binding site itself, rather than from an effect on the ability of the RA Ab to transmit a putative conformational "signal" from the Ag-binding site to the C1 binding site. Finally, our data show that the observed functional effect of reduction and alkylation depends strongly on the assay used to evaluate that effect.

Alkylation↗
PubMed1991

Effect of N-alkyl substituents on the DNA binding properties of meso-tetrakis (4-N-alkylpyridinium-4-yl)porphyrins and their nickel derivatives.

Resonance Raman, NMR, and visible spectroscopies, as well as viscosity and equilibrium dialysis studies were used to assess the effect of the N-alkyl substituent of meso-tetrakis(4-N-alkylpyridinium-4-yl)porphyrin cations on DNA binding. The DNAs studied include the native DNA, calf thymus DNA (CT DNA), the synthetic polynucleotides [poly(dGdC)]2 and [poly(dAdT)]2, and the oligonucleotide d(TATACGTATA)2. Both the porphyrins and the metalloporphyrins containing Ni(II) were examined with the N-alkyl = propyl (TPrpyP(4) and NiTPrpyP(4)) and 2-hydroxyethyl (TEtOHpyP(4) and NiTEtOHpyP(4)). The results were compared to those from the parent porphyrins with the N-methyl substituent (TMpyP(4) and NiTMpyP(4)). For almost all the comparisons made, the new porphyrin cations gave results very similar to those for the TMpyP(4) species. The resonance Raman study indicated that for the three DNA polymers all the Ni species were in the four-coordinate form when bound to all three polymers. It is suggested that both TPrpyP(4) and TEtOHpyP(4) bind to GC regions of DNA in the same intercalative manner as TMpyP(4) with the N-alkyl substituent extended into the solvent. For AT regions of DNA, the binding of TPrpyP(4) and TEtOHpyP(4) is nonintercalative, as found previously for TMpyP(4). The NiPrpy(4) and NiTEtOHpyP(4) cations bind to these polymers in a similar manner to the apo-porphyrins. The similar Raman spectral changes for the three Ni porphyrins upon addition of [poly(dAdT)]2 suggest that partial intercalation is not occurring because models indicate that it would be difficult to accommodate the bulkier N-alkyl substituents.

Alkylation↗