Computational estimation of the acidities of purines and indoles

Kara L. Geremia1 & Paul G. Seybold1

Received: 1 August 2018 / Accepted: 4 December 2018 / Published online: 3 January 2019
# Springer-Verlag GmbH Germany, part of Springer Nature 2019

 

Introduction

The purines comprise a key class of biochemically active compounds, and the purine skeleton is said to be Bthe most widely distributed N-heterocycle in nature^ [1]. Although best known for containing the nucleobases adenine and guanine, the purines, along with related compounds such as the indoles, encompass an enormous diversity of bioactive compounds, ranging from natural products to medicines and pharmaceuticals. Accordingly, it is useful to develop theoretical methods for estimating the physical and chemical properties of these compounds. In particular, the acidities of these compounds— as expressed by their pKa values—are of special interest since, among other things, these values determine the particular forms (neutral and ionic) that will prevail under different circumstances.

Several theoretical approaches can be taken when es- timating the pKa values of chemical compounds [2–7]. In   a first-principles approach, one directly employs quantum-chemical methods and solvent models indepen- dent of experimental data, which has the  disadvantage that quite demanding computational methods are general- ly required to achieve reasonable accuracy [2, 8, 9]. In some cases, improvements can be obtained by adding explicit solvent molecules to the calculations (see, e.g., Adam [10] and Thapa and Schlegel [11]). Quantitative structure–activity relationship (QSAR) methods [4, 12–14] search for molecular features (Bdescriptors^)  associated with specific molecular properties such as the pKa, and thus rely on existing experimental data, but at  the same time such methods allow the use of less demanding computational levels. In addition, QSAR methods typi- cally produce general equations that can be applied to other related compounds beyond those in the initial test  set. A third approach, used in a number of commercial programs, relies on a large database of experimental values and substituent features such as Hammett con- stants to estimate molecular pKa values [15, 16]. In this report, we employ the latter two methods to estimate the pKa values of a collection of purines and related com- pounds and to provide QSAR equations for wider appli- cation to this class of compounds.

The atom numbering scheme for purines is somewhat idiosyncratic [17], as it treats the purine framework as a six-membered pyrimidine ring fused to an imidazole ring, whereas the more customary atom numbering scheme is used for the heterocyclic rings in indoles. These schemes are shown below.

In the initial stage of this study, experimental data for the pKa values of selected compounds—purines and related ring heterocycles such as indoles in the present case—were col- lected. The pKa values given in the literature for the 31 select- ed compounds are shown in Table 1. Here we define the cation→ neutral dissociation as pKa1 and the neutral → anion dis- sociation as pKa2. Also included in this table for comparison purposes are the pKa values determined via the Advanced Chemical Development (ACD/Labs, Toronto, Canada) PhysChem Suite commercial program.

 

A complication arises for the nitrogen heterocyclic ring systems studied in this work because these compounds typi- cally exist in a variety of tautomeric forms [18–21]. We have used density functional theory B3LYP/6–31 + G** computa- tions as implemented by the Spartan’10 computational pro- gram (Wavefunction, Inc., Irvine, CA, USA) along with the aqueous SM8 solvent model of Marenich et al. [22] to study the relative stabilities of the possible tautomers of each com- pound. (These studies will be reported in the future.) For sim- plicity, for dissociations 1 and 2, we assumed that the most stable tautomer (as determined computationally) of each spe- cies (cation or neutral) is the dissociating species. [For exam- ple, the 1,9(H)-P+ form of the basic purine cation species, protonated at the 1 and 9 positions, is computed to be the most stable cation tautomer in aqueous solution; in process 1, this species dissociates to form the most stable neutral tautomer 9H-P, which is protonated at nitrogen 9, and this in turn dissociates in process 2 to form the anion P− with none of the ring nitrogen atoms protonated.

 

We were first interested in ascertaining whether the B3LYP/6–31 + G** level of theory was adequate for accurate- ly determining the pKa values of these compounds using the relation ΔG°= -RTpKa. The Spartan’10 computational pro- gram cannot evaluate the Gibbs energy change in solution because of the complications introduced by solute–solvent interactions, but calculations of ΔG° can be tested against gas-phase data where available. The NIST chemical database[23] lists experimental gas-phase ΔrG° values for the reaction A− + H+ ⇌ AH for five of the compounds listed in Table 1. (The vacuum Gibbs energy G°(H+) is −26.3 kJ/mol at 298.15K [5].) The experimental and calculated ΔrG°= G°(A−)+ G°(H+) − G°(HA) values are shown in Table 2. The experimental and calculated ΔrG° values are seen to be in excellent agreement and are strongly correlated (R2 = 0.996), supporting the use of the present level of computation. As noted, it is not possible to calculate G° values directly within a solvent using the Spartan program, so we wished to find a surrogate descriptor for the pKa regression calculations. The energy change ΔE has previously been used successfully in a number of studies, and was deemed a reasonable descrip- tor candidate [24–26]. To examine this connection further, we determined the correlation between the calculated vacuum ΔE values and the experimental gas-phase ΔGr° value for the compounds in Table 2. The correlation was found to be excel- lent (R2 = 0.999), further supporting the premise that ΔE could serve as a surrogate for ΔG° under more general conditions, e.g., within the solvent environment. 

 

Results and discussion

In some earlier studies of more uniform series of compounds [24, 27, 28], vacuum-only calculations provided quite accu- rate accounts of pKa variations, so we were first interested to see whether this might also hold for the present compounds. Nineteen values for pKa1 in aqueous solution were found in the literature, and when these were tested, four compounds (indole, indoline, 7-azaindole, and diphenylamine) stood out as obvious outliers. Outliers in QSAR studies can be quite informative, in some cases showing weaknesses in the theo- retical regression model and in other cases alerting observers to deviations from the underlying experimental behaviors assumed for the sample compounds (see, e.g., [21, 29]). In the present case, all four outliers were clearly exceptions in some way from the general aromatic N-heterocyclic nitrogen acid systems that form the focus of this study. The indole cation is known to be protonated on a ring carbon, and therefore disso- ciates as a carbon acid rather than as a nitrogen acid [30]. Indoline dissociates from a saturated ring portion of its molec- ular skeleton. 7-Azaindole is well known to dimerize strongly due to hydrogen bonding [31–33], and is—according to Koyama and Wakisaka [34]—unlikely to appear as a monomer unit except under extreme conditions. Diphenylamine is a moderately flexible, nonplanar compound, unlike the planar aromatic systems of the remaining compounds.

After removing the four outliers, the descriptor ΔEVAC was tested against the experimental aqueous pKa values and showed a significant but still modest correlation (n = 15,  R2 = 0.829, s = 1.46, F = 63, where n is the number of com- pounds, R2 is the coefficient of determination, s is the standard error of the estimate, and F is the Fisher statistic).

The experimental pKa values studied here were mea- sured in aqueous solution. Re-optimization of the com- pound structures within the aqueous SM8 solvent model  of Marenich et al. [22] produced a greatly improved relationship for pKa1: These results are plotted in Fig. 1. This improvement reinforces results from earlier studies which showed that com- pounds can assume quite different conformations in solution from those in vacuum, and that solvent–solute interactions can significantly influence the molecular acidity [26, 29].

 

Upon examination of the compounds for the neutral → an- ion dissociation (pKa2), three compounds were removed as outliers: caffeine, paraxanthine, and  theobromine.  Because caffeine lacks a free ring –NH– group for dissociation, it is generally assumed not to function as an acid in its neutral form [35, 36]. (Nonetheless, pKa values ranging from 10.4 to 14 have appeared in the literature [37, 38], although the specific disso- ciations in question were not identified.) Paraxanthene and theobromine are caffeine metabolites, and the reason(s) for their deviations from expected behavior are presently unknown.

These data are plotted in Fig. 2. We note that the t tests for both the variable and constant terms in Eqs. 1 and 2 show high significance for these terms.

Although we have generally relied on single-descriptor models for pKa values, in some cases including additional de- scriptors can supplement and improve the regression model. A possible supplemental descriptor is ΔQN, the change in the natural charge [39] on the dissociating nitrogen atom upon the loss of the proton. By itself, this descriptor shows only a very modest correlation (R2 = 0.446) with pKa2. However, adding this descriptor to ΔEH2O significantly improves the pKa2 regression:

Here, the Fisher statistic more than doubles, supporting the addition of the second descriptor. (Even adding a highly correlated descriptor, which might be expected to add little new information, can sometimes considerably improve the regression performance [40, 41].) Table 3 compares the calculated and experimental results for these compounds. No experimental values were found in the literature for some of the compounds of interest in this work, so the  computed  results  given here can provide reasonable estimates for  those  absent pKa values. This applies in particular to compounds  such as isatin, isoindole, oxindole, phthalimide, uric acid, and 9-methyluric acid, which are expected to display strongly negative pKa1 values, but also to compounds such as benzimidizoline and indoline that have high pKa2 values.

Results obtained from the commercial ACD PhysChem Suite (see Table 1) also showed excellent correlations with the experimental values for both pKa1 (R2 = 0.948) and for pKa2 (R2 = 0.957), implying that this program can be used despite its inability to identify carbon acid disso- ciations (e.g., for the indole cation, which it treats as a nitrogen dissociation).

Conclusions

The parameter pKa is a crucial physicochemical property that impacts a variety of important chemical outcomes [42]. A means for accurately estimating pKa values com- putationally would therefore be very useful for biochemical and pharmaceutical applications. It was shown in this work that the utilization of a relatively modest computa- tional level (B3LYP/6–31 + G**) and a widely available aqueous solvent model allows accurate QSAR estimates of pKa1 and pKa2 to be made for purines, indoles, and related compounds. Exceptions are generally due to obvious deviations from the common aromatic ring N–H dissociation process of this class, so it is important to be alert to the possible participation of alternative dissociation modes for some compounds.

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2-Amino-n-ethylpropanamide, HCl Catalog No.:AA00982G CAS No.:1078162-88-5 MDL No.:MFCD09971350 MF:C5H13ClN2O MW:152.6225	N-(4-bromophenyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019LBS CAS No.:1078162-91-0 MDL No.:MFCD09863853 MF:C11H14BrClN2O MW:305.5987
N-(furan-2-ylmethyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019LD7 CAS No.:1078162-92-1 MDL No.:MFCD09971403 MF:C10H15ClN2O2 MW:230.6913	N-(1,3-benzothiazol-2-yl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019LDJ CAS No.:1078162-93-2 MDL No.:MFCD09971410 MF:C12H14ClN3OS MW:283.7771
N-phenyl-1,3-thiazolidine-4-carboxamide hydrochloride Catalog No.:AA019LEB CAS No.:1078162-97-6 MDL No.:MFCD09971432 MF:C10H13ClN2OS MW:244.7410	1-Amino-3-morpholin-4-ylpropan-2-ol oxalate Catalog No.:AA00HAYO CAS No.:1078162-98-7 MDL No.:MFCD09971449 MF:C9H18N2O6 MW:250.2490
N-benzyl-1,3-thiazolidine-4-carboxamide hydrochloride Catalog No.:AA019LFC CAS No.:1078162-99-8 MDL No.:MFCD09971460 MF:C11H15ClN2OS MW:258.7676	N-1,3-Thiazol-2-ylpyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019LGX CAS No.:1078163-00-4 MDL No.:MFCD09971500 MF:C8H12ClN3OS MW:233.7184
3-Ethyl 5-methyl 2-[(2-aminoethoxy)methyl]-6-methyl-4-phenyl-1,4-dihydropyridine-3,5-dicarboxylate benzenesulfonate Catalog No.:AA019LKY CAS No.:1078163-17-3 MDL No.:MFCD09971580 MF:C26H32N2O8S MW:532.6059	4-(1,3-thiazolidine-4-carbonyl)morpholine hydrochloride Catalog No.:AA019LMG CAS No.:1078163-18-4 MDL No.:MFCD09971611 MF:C8H15ClN2O2S MW:238.7349
N-(2,2,2-trifluoroethyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019LVX CAS No.:1078163-20-8 MDL No.:MFCD09971635 MF:C7H12ClF3N2O MW:232.6312	N-(2,4-Dichlorophenyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019M9O CAS No.:1078163-21-9 MDL No.:MFCD10686757 MF:C11H13Cl3N2O MW:295.5927
N-(3,5-dichlorophenyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019M9P CAS No.:1078163-22-0 MDL No.:MFCD10686758 MF:C11H13Cl3N2O MW:295.5927	N-(2,5-dichlorophenyl)pyrrolidine-2-carboxamide hydrochloride Catalog No.:AA019MA2 CAS No.:1078163-23-1 MDL No.:MFCD10686764 MF:C11H13Cl3N2O MW:295.5927
N-(3,4-dichlorophenyl)piperidine-2-carboxamide hydrochloride Catalog No.:AA019MAB CAS No.:1078163-24-2 MDL No.:MFCD10686769 MF:C12H15Cl3N2O MW:309.6193	N-(2,4-dichlorophenyl)piperidine-2-carboxamide hydrochloride Catalog No.:AA019MAC CAS No.:1078163-25-3 MDL No.:MFCD10686770 MF:C12H15Cl3N2O MW:309.6193
N-(3,5-difluorophenyl)piperidine-2-carboxamide hydrochloride Catalog No.:AA019MAV CAS No.:1078163-26-4 MDL No.:MFCD10686782 MF:C12H15ClF2N2O MW:276.7101	PF 04418948 Catalog No.:AA008TK4 CAS No.:1078166-57-0 MDL No.:MFCD24387541 MF:C23H20FNO5 MW:409.4070
Methyl thieno[2,3-c]pyridine-7-carboxylate Catalog No.:AA00HAYP CAS No.:1078167-97-1 MDL No.:MFCD11975119 MF:C9H7NO2S MW:193.2224	1H-Imidazo[4,5-c]pyridine-4-carbonitrile Catalog No.:AA0094N7 CAS No.:1078168-19-0 MDL No.:MFCD17015949 MF:C7H4N4 MW:144.1335
Thieno[3,2-b]pyridin-7-ol Catalog No.:AA0035LZ CAS No.:107818-20-2 MDL No.:MFCD01863636 MF:C7H5NOS MW:151.1857	methyl 3-amino-5-(2-chlorophenyl)thiophene-2-carboxylate Catalog No.:AA00975T CAS No.:107818-29-1 MDL No.:MFCD11207952 MF:C12H10ClNO2S MW:267.7313
Methyl 3-amino-5-bromothiophene-2-carboxylate Catalog No.:AA008478 CAS No.:107818-55-3 MDL No.:MFCD12031265 MF:C6H6BrNO2S MW:236.0863	1,3-Di-boc-2-methylisothiourea Catalog No.:AA0038WP CAS No.:107819-90-9 MDL No.:MFCD00239356 MF:C12H22N2O4S MW:290.3791
L-Valine chloromethyl ketone hydrochloride Catalog No.:AA009503 CAS No.:107831-79-8 MDL No.:MFCD11113163 MF:C6H13Cl2NO MW:186.0795	Nicorandil N-Oxide Catalog No.:AA008X47 CAS No.:107833-98-7 MDL No.:MFCD18382405 MF:C8H9N3O5 MW:227.1742
4-(2-Thienyl)benzaldehyde Catalog No.:AA003K7Y CAS No.:107834-03-7 MDL No.:MFCD02682003 MF:C11H8OS MW:188.2456	(2E)-3-Amino-3-(4-chlorophenyl)prop-2-enenitrile Catalog No.:AA00IYPF CAS No.:107840-43-7 MDL No.:MFCD01871636 MF:C9H7ClN2 MW:178.6183
5-Amino-4-cyano-1-(3-chlorophenyl)-3-methylpyrazole Catalog No.:AA008470 CAS No.:107842-57-9 MDL No.:MFCD11053835 MF:C11H9ClN4 MW:232.6690	(E)-Benzyl 3-(3,4-dihydroxyphenyl)acrylate Catalog No.:AA008U4C CAS No.:107843-77-6 MDL No.:MFCD09752937 MF:C16H14O4 MW:270.2800
5-Amino-4-cyano-1-(2-chlorophenyl)-3-methylpyrazole Catalog No.:AA00845L CAS No.:107856-31-5 MDL No.:MFCD10699686 MF:C11H9ClN4 MW:232.6690	2-amino-3-{1H-pyrrolo[2,3-b]pyridin-1-yl}propanoic acid hydrochloride Catalog No.:AA019XGM CAS No.:1078566-95-6 MDL No.:MFCD09971778 MF:C10H12ClN3O2 MW:241.6742
2-(Hydroxymethyl)pyridine-5-boronic acid, pinacol ester Catalog No.:AA00845K CAS No.:1078575-71-9 MDL No.:MFCD12025438 MF:C12H18BNO3 MW:235.0872	Ethyl 3-(4-(hydroxymethyl)phenyl)propanoate Catalog No.:AA007VHX CAS No.:107859-98-3 MDL No.:MFCD09028871 MF:C12H16O3 MW:208.2536
ethyl (2S)-4-methyl-2-[N-methyl4-(aminomethyl)benzenesulfonamido]pentanoate hydrochloride Catalog No.:AA00IPVL CAS No.:1078603-54-9 MDL No.:MFCD04035621 MF:C16H27ClN2O4S MW:378.9146	ethyl 1-thia-4-azaspiro[4.5]decane-3-carboxylate hydrochloride Catalog No.:AA00IPQ6 CAS No.:1078603-72-1 MDL No.:MFCD06795604 MF:C11H20ClNO2S MW:265.8000
Cyclohexanecarboxylic acid, 3-acetyl-4-oxo-, ethyl ester Catalog No.:AA00HAYR CAS No.:107861-64-3 MDL No.:MFCD23978405 MF:C11H16O4 MW:212.2423	(2,3,4,6-tetrafluorophenyl)methanaminium chloride Catalog No.:AA00HAYS CAS No.:1078610-94-2 MDL No.:MFCD06199158 MF:C7H6ClF4N MW:215.5759
Methyl amino(3,4-dichlorophenyl)acetate hydrochloride Catalog No.:AA003RJK CAS No.:1078611-21-8 MDL No.:MFCD04115512 MF:C9H10Cl3NO2 MW:270.5402	2,6-Dichloropyridine-3-sulfonamide Catalog No.:AA01A8KV CAS No.:1078627-77-6 MDL No.:MFCD15142801 MF:C5H4Cl2N2O2S MW:227.0685
(2,4-dimethylphenyl)methanesulfonamide Catalog No.:AA00IWHX CAS No.:1078627-79-8 MDL No.:MFCD16671939 MF:C9H13NO2S MW:199.2700	(3,4-dimethylphenyl)methanesulfonamide Catalog No.:AA01B7PV CAS No.:1078627-81-2 MDL No.:MFCD14690629 MF:C9H13NO2S MW:199.2700
N-methylmethanaminium 4-cyano-1H-pyrazole-5-carboxylate Catalog No.:AA00IYBD CAS No.:1078634-01-1 MDL No.:MFCD02661869 MF:C7H10N4O2 MW:182.1799	6-chloro-3-(2-chloro-2,2-difluoroacetyl)imidazo[1,2-a]pyridin-4-ium 2-chloro-2,2-difluoroacetate Catalog No.:AA00ISG9 CAS No.:1078634-12-4 MDL No.:MFCD06795629 MF:C11H8Cl3F4N2O3 MW:398.5454
{[(4-chloro-2-methyl-5-oxo-1-phenyl-2,5-dihydro-1H-pyrazol-3-yl)methyl]sulfanyl}methanimidamide hydrobromide Catalog No.:AA00IZVA CAS No.:1078634-31-7 MDL No.:MFCD01114546 MF:C12H14BrClN4OS MW:377.6878	{[amino(prop-2-yn-1-ylsulfanyl)methylidene]amino}[(4-fluorophenyl)methylidene]amine hydrochloride Catalog No.:AA00IV2D CAS No.:1078634-39-5 MDL No.:MFCD04152261 MF:C11H11ClFN3S MW:271.7415
3-Hydroxy-3-(2-oxopropyl)-1-propylindolin-2-one Catalog No.:AA00845G CAS No.:107864-79-9 MDL No.:MFCD01817193 MF:C14H17NO3 MW:247.2897	4-(3-Aminophenyl)phenol Catalog No.:AA008UQF CAS No.:107865-00-9 MDL No.:MFCD04117374 MF:C12H11NO MW:185.2218
1-Acetyl-1h-1,2,3-triazolo[4,5-b]pyridine Catalog No.:AA003DTF CAS No.:107866-54-6 MDL No.:MFCD00075383 MF:C7H6N4O MW:162.1487	2-(4-oxo-4,5,6,7-tetrahydro-1-benzothiophen-5-yl)acetic acid Catalog No.:AA01BIEF CAS No.:107866-80-8 MDL No.:MFCD24479945 MF:C10H10O3S MW:210.2496
5-(Trifluoromethyl)pyridine-2,3-diamine Catalog No.:AA00HAYT CAS No.:107867-51-6 MDL No.:MFCD10696252 MF:C6H6F3N3 MW:177.1271	(8R,9S,10R,13S,14S)-10,13-Dimethyl-6-methylene-7,8,9,11,12,13,15,16-octahydro-6H-cyclopenta[a]phenanthrene-3,17(10H,14H)-dione Catalog No.:AA003BWA CAS No.:107868-30-4 MDL No.:MFCD00866994 MF:C20H24O2 MW:296.4034
(3aR,6S)-8,8-dimethyl-4,5,6,7-tetrahydro-3h-3a,6-methanobenzo[c]isothiazole 2,2-dioxide Catalog No.:AA003B98 CAS No.:107869-45-4 MDL No.:MFCD00064576 MF:C10H15NO2S MW:213.2966	2-(Pyrimidin-5-yl)benzoic acid Catalog No.:AA00HAYU CAS No.:1078712-00-1 MDL No.:MFCD11932686 MF:C11H8N2O2 MW:200.1934
(R,R)-Cilastatin Catalog No.:AA01DZG9 CAS No.:107872-23-1 MDL No.: MF:C26H34O8 MW:474.5434	5,5-dimethyl-2-oxohexanoic acid Catalog No.:AA01BHMZ CAS No.:107872-85-5 MDL No.:MFCD20639673 MF:C8H14O3 MW:158.1950
2,2-Difluorocyclopropanecarboxylic acid Catalog No.:AA003F85 CAS No.:107873-03-0 MDL No.:MFCD04115828 MF:C4H4F2O2 MW:122.0702	FaMotidine Acid IMpurity Catalog No.:AA008WRO CAS No.:107880-74-0 MDL No.:MFCD06208403 MF:C8H12N4O2S2 MW:260.3365
methyl 1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)quinoline-3-carboxylate Catalog No.:AA008TOK CAS No.:107884-23-1 MDL No.:MFCD27578272 MF:C18H20FN3O3 MW:345.3681	2-methoxy-3-methylbutanal Catalog No.:AA01AMOL CAS No.:107889-83-8 MDL No.:MFCD24681544 MF:C6H12O2 MW:116.1583
1-[4-(Trifluoromethyl)benzyl]piperazine Catalog No.:AA008V74 CAS No.:107890-32-4 MDL No.:MFCD03407490 MF:C12H15F3N2 MW:244.2561	2-Imidazolidinone, 1-(2-hydroxypropyl)- Catalog No.:AA00845D CAS No.:107890-85-7 MDL No.:MFCD19220807 MF:C6H12N2O2 MW:144.1717
Benzoic acid-d5 Catalog No.:AA008RGA CAS No.:1079-02-3 MDL No.:MFCD00002400 MF:C7HD5O2 MW:127.1521	Alpha,alpha',2,3,5,6-hexachloro-p-xylene Catalog No.:AA003NOH CAS No.:1079-17-0 MDL No.:MFCD00000894 MF:C8H5Cl7 MW:349.2963
[1,1'-Biphenyl]-2,5-diol Catalog No.:AA003HSR CAS No.:1079-21-6 MDL No.:MFCD00002342 MF:C12H10O2 MW:186.2066	2,3,4,9-Tetrahydro-1h-carbazol-6-amine hydrochloride Catalog No.:AA019LIX CAS No.:1079-26-1 MDL No.:MFCD01739721 MF:C12H15ClN2 MW:222.7139
Methyl 5-chloro-1H-indazole-3-carboxylate Catalog No.:AA003RUR CAS No.:1079-46-5 MDL No.:MFCD07371574 MF:C9H7ClN2O2 MW:210.6171	Methyl 5-iodo-1h-indazole-3-carboxylate Catalog No.:AA008QY6 CAS No.:1079-47-6 MDL No.:MFCD07371578 MF:C9H7IN2O2 MW:302.0686
Chlorodiphenylphosphine Catalog No.:AA0034IQ CAS No.:1079-66-9 MDL No.:MFCD00000529 MF:C12H10ClP MW:220.6346	1,2,3,4,5,6,7,8-OCTAHYDROANTHRACENE Catalog No.:AA008YAW CAS No.:1079-71-6 MDL No.:MFCD00021091 MF:C14H18 MW:186.2927
6-(4-Chlorophenyl)-4,5-dihydropyridazin-3(2h)-one Catalog No.:AA007DM1 CAS No.:1079-73-8 MDL No.:MFCD00276381 MF:C10H9ClN2O MW:208.6443	2,6-Dimethyl-3,5-diacetyl-1,4-dihydropyridine Catalog No.:AA00844H CAS No.:1079-95-4 MDL No.:MFCD00005952 MF:C11H15NO2 MW:193.2423
3-amino-2-methylpropane-1,2-diol Catalog No.:AA019SWM CAS No.:107903-33-3 MDL No.:MFCD19208900 MF:C4H11NO2 MW:105.1356	4-oxa-1-azabicyclo[3.3.1]nonan-6-one Catalog No.:AA01AUY8 CAS No.:107904-15-4 MDL No.:MFCD24696074 MF:C7H11NO2 MW:141.1677
Glycodeoxycholic Acid monohydrate Catalog No.:AA01EAVD CAS No.:1079043-81-4 MDL No.:MFCD00150922 MF:C26H45NO6 MW:467.6386	Ethyl 2-[Bis(2,2,2-trifluoroethyl)phosphono] Propionate Catalog No.:AA007DO3 CAS No.:107905-52-2 MDL No.:MFCD04039536 MF:C9H13F6O5P MW:346.1607
5-Amino-6-methylpicolinonitrile Catalog No.:AA007VH2 CAS No.:1079054-78-6 MDL No.:MFCD08062828 MF:C7H7N3 MW:133.1506	Ganciclovir sodium Catalog No.:AA019FT1 CAS No.:107910-75-8 MDL No.:MFCD00873979 MF:C9H12N5NaO4 MW:277.2124
N,N-Diethyl-n-methyl-n-(2-methoxyethyl)ammonium imidodisulfuryl fluoride Catalog No.:AA00HAYZ CAS No.:1079129-48-8 MDL No.:MFCD22421701 MF:C8H20F2N2O5S2 MW:326.3816	(5E)-2-Mercapto-5-(2-naphthylmethylene)-1,3-thiazol-4(5h)-one Catalog No.:AA008453 CAS No.:107916-92-7 MDL No.:MFCD04969039 MF:C14H9NOS2 MW:271.3574
4-(1-Methyl-1h-pyrazol-4-yl)aniline Catalog No.:AA008VE9 CAS No.:1079178-22-5 MDL No.:MFCD06797404 MF:C10H11N3 MW:173.2144	[(2,5-dimethylphenyl)methyl](methyl)amine Catalog No.:AA01BE1D CAS No.:1079178-90-7 MDL No.:MFCD11204737 MF:C10H15N MW:149.2328
2-Chloro-3-fluoro-5-nitropyridine Catalog No.:AA008452 CAS No.:1079179-12-6 MDL No.:MFCD16659664 MF:C5H2ClFN2O2 MW:176.5330	ethyl 4-[(3,4-dichlorophenyl)amino]-2-(methylsulfanyl)pyrimidine-5-carboxylate Catalog No.:AA00IVIS CAS No.:107920-54-7 MDL No.:MFCD01444031 MF:C14H13Cl2N3O2S MW:358.2429
Methyl 4-benzenesulfonamidobenzoate Catalog No.:AA007VH0 CAS No.:107920-79-6 MDL No.:MFCD00591212 MF:C14H13NO4S MW:291.3223	Methyl 3-benzenesulfonamidobenzoate Catalog No.:AA00944M CAS No.:107922-46-3 MDL No.:MFCD00121318 MF:C14H13NO4S MW:291.3223
2-(3H-Imidazo[4,5-b]pyridin-2-yl)acetonitrile Catalog No.:AA007DNX CAS No.:107932-97-8 MDL No.:MFCD05861393 MF:C8H6N4 MW:158.1600	Ethyl 2-(3h-imidazo[4,5-b]pyridin-2-yl)acetate Catalog No.:AA01DX79 CAS No.:107932-98-9 MDL No.:MFCD21935249 MF:C10H11N3O2 MW:205.2132
1H-Imidazo[4,5-b]pyridine-2-ethanimidamide, N-hydroxy- Catalog No.:AA01AK4O CAS No.:107933-05-1 MDL No.:MFCD05721713 MF:C8H9N5O MW:191.1900	Imidazo[1,2-a]pyridin-2(3H)-one hydrobromide Catalog No.:AA009TBH CAS No.:107934-07-6 MDL No.:MFCD00226053 MF:C7H7BrN2O MW:215.0473
9,9-Bis(4-amino-3-methylphenyl)fluorene Catalog No.:AA003NGW CAS No.:107934-60-1 MDL No.:MFCD04038168 MF:C27H24N2 MW:376.4929	9,9-Bis(4-amino-3-chlorophenyl)fluorene Catalog No.:AA003K9V CAS No.:107934-68-9 MDL No.:MFCD10000948 MF:C25H18Cl2N2 MW:417.3298
2-chloro-4-(trifluoromethoxy)benzaldehyde Catalog No.:AA0093WX CAS No.:1079351-20-4 MDL No.:MFCD18393768 MF:C8H4ClF3O2 MW:224.5644	5-bromo-2-(difluoromethoxy)-4-methylpyridine Catalog No.:AA01DH16 CAS No.:1079352-13-8 MDL No.:MFCD14698387 MF:C7H6BrF2NO MW:238.0294
2-chloro-4-(methylsulfanyl)benzoic acid Catalog No.:AA01DUVM CAS No.:1079360-49-8 MDL No.:MFCD17256624 MF:C8H7ClO2S MW:202.6580	N'-hydroxy-4-methoxybenzene-1-carboximidamide Catalog No.:AA019UFT CAS No.:1079393-88-6 MDL No.:MFCD00816993 MF:C8H10N2O2 MW:166.1772
5-(1H-Imidazol-1-yl)pyrimidine Catalog No.:AA019YCE CAS No.:1079394-95-8 MDL No.:MFCD22056416 MF:C7H6N4 MW:146.1493	1,2,5-Oxadiazole-3-carbonyl chloride Catalog No.:AA00HAZ7 CAS No.:1079401-91-4 MDL No.:MFCD02853071 MF:C3HClN2O2 MW:132.5052
4,4,5,5-tetramethyl-2-[2-(2,2,2-trifluoroethyl)phenyl]-1,3,2-dioxaborolane Catalog No.:AA01B74Q CAS No.:1079402-24-6 MDL No.:MFCD18734058 MF:C14H18BF3O2 MW:286.0977	5-Methoxy-2-(trifluoromethoxy)phenylboronic acid Catalog No.:AA007VGU CAS No.:1079402-25-7 MDL No.:MFCD12025981 MF:C8H8BF3O4 MW:235.9529
2-[5-fluoro-2-(2,2,2-trifluoroethoxy)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane Catalog No.:AA01BCIP CAS No.:1079402-39-3 MDL No.:MFCD22494245 MF:C14H17BF4O3 MW:320.0876	5-Methyl-2-(trifluoromethoxy)phenylboronic acid Catalog No.:AA00HAZ8 CAS No.:1079402-45-1 MDL No.:MFCD18399838 MF:C8H8BF3O3 MW:219.9535
4-Chloro-3-(1H-pyrrol-1-yl)benzoic acid Catalog No.:AA008VFF CAS No.:107946-72-5 MDL No.:MFCD04363490 MF:C11H8ClNO2 MW:221.6397	5-(Pyrrolidin-1-yl)nicotinic acid Catalog No.:AA00VV07 CAS No.:107946-76-9 MDL No.:MFCD06254780 MF:C10H12N2O2 MW:192.2145
2-(benzylamino)-5-nitrobenzoic acid Catalog No.:AA00IT0Z CAS No.:107946-93-0 MDL No.:MFCD01788145 MF:C14H12N2O4 MW:272.2561	Methyl 3-bromo-4-chlorobenzoate Catalog No.:AA00844T CAS No.:107947-17-1 MDL No.:MFCD09751943 MF:C8H6BrClO2 MW:249.4890
Trans-1-[(4-ethylphenyl)ethynyl]-4-(4-propylcyclohexyl)benzene Catalog No.:AA00906Y CAS No.:107949-21-3 MDL No.:MFCD11053405 MF:C25H30 MW:330.5057	2-(4-methoxyphenoxy)-N-[(phenylcarbamothioyl)amino]acetamide Catalog No.:AA00ITBM CAS No.:107951-85-9 MDL No.:MFCD00245276 MF:C16H17N3O3S MW:331.3895
5-[(4-methoxyphenoxy)methyl]-4-phenyl-4H-1,2,4-triazole-3-thiol Catalog No.:AA007DNR CAS No.:107951-97-3 MDL No.:MFCD01809838 MF:C16H15N3O2S MW:313.3742	6-Bromo-2,5-dioxo-1,2,5,6,7,8-hexahydroquinoline-3-carbonitrile Catalog No.:AA008ROG CAS No.:107955-83-9 MDL No.:MFCD00829040 MF:C10H7BrN2O2 MW:267.0788
Benzeneacetamide, N-hydroxy-a,a-dimethyl- Catalog No.:AA019WNZ CAS No.:107955-92-0 MDL No.:MFCD09929777 MF:C10H13NO2 MW:179.2157	2,4-Dichloro-6-isopropyl-5h-pyrrolo[3,4-d]pyrimidin-7(6h)-one Catalog No.:AA0094F3 CAS No.:1079649-94-7 MDL No.:MFCD22571540 MF:C9H9Cl2N3O MW:246.0933
(R)-1-(3-Fluoro-4-(trifluoromethyl)phenyl)ethanamine Catalog No.:AA00964O CAS No.:1079656-75-9 MDL No.:MFCD06762190 MF:C9H9F4N MW:207.1681	2-(4-aminophenyl)-N-ethylacetamide Catalog No.:AA019LXB CAS No.:107966-09-6 MDL No.:MFCD09043009 MF:C10H14N2O MW:178.2310
2-(2-Methoxyphenoxy)acetohydrazide Catalog No.:AA00844N CAS No.:107967-88-4 MDL No.:MFCD00553729 MF:C9H12N2O3 MW:196.2032	Butanoic acid, 4-hydroxy-2,2-dimethyl-, monosodium salt Catalog No.:AA01FM54 CAS No.:107975-81-5 MDL No.:MFCD30486076 MF:C6H11NaO3 MW:154.1395
sodium 4-hydroxy-2-methylbutanoate Catalog No.:AA01EM9K CAS No.:107975-82-6 MDL No.:MFCD31666085 MF:C5H9NaO3 MW:140.1129	tert-butyl 4-methylpyridine-3-carboxylate Catalog No.:AA01C3ST CAS No.:107977-28-6 MDL No.:MFCD18206160 MF:C11H15NO2 MW:193.2423
tert-Butyl n-[(2,5-difluorobenzoyl)amino]-carbamate Catalog No.:AA008U73 CAS No.:1079843-62-1 MDL No.:MFCD23700206 MF:C12H14F2N2O3 MW:272.2480	2-Acetamido-4-bromophenol Catalog No.:AA003G7L CAS No.:107986-49-2 MDL No.:MFCD02933327 MF:C8H8BrNO2 MW:230.0586
N-Acetyl-S-(3-aMino-2-hydroxy-3-oxopropyl)-L-cysteine-1,1-diMethylethyl Ester Catalog No.:AA008X3R CAS No.:1079950-08-5 MDL No.:MFCD28899035 MF:C12H22N2O5S MW:306.3785	N-Acetyl-S-[2-aMino-1-(hydroxyMethyl)-2-oxoethyl]-L-cysteine-1,1-diMethylethyl Ester Catalog No.:AA008VU3 CAS No.:1079950-10-9 MDL No.:MFCD31562302 MF:C12H22N2O5S MW:306.3785
(2-Methyl-2h-indazol-4-yl)methanol Catalog No.:AA00HAZD CAS No.:107999-26-8 MDL No.:MFCD12028586 MF:C9H10N2O MW:162.1885	6-Fluoro-2-methyl-3-nitrobenzoic acid Catalog No.:AA003ADM CAS No.:1079992-96-3 MDL No.:MFCD28347722 MF:C8H6FNO4 MW:199.1359
Methyl 6-fluoro-2-methyl-3-nitrobenzoate Catalog No.:AA00HAZE CAS No.:1079992-97-4 MDL No.:MFCD28347723 MF:C9H8FNO4 MW:213.1625	Methyl 3-amino-4-fluoro-2-methylbenzoate Catalog No.:AA01FR1L CAS No.:1079993-18-2 MDL No.:MFCD24643109 MF:C9H10FNO2 MW:183.1796
N,N-Dimethylethylenediamine Catalog No.:AA00337J CAS No.:108-00-9 MDL No.:MFCD00008175 MF:C4H12N2 MW:88.1515	N,N-Dimethylethanolamine Catalog No.:AA0032SP CAS No.:108-01-0 MDL No.:MFCD00002846 MF:C4H11NO MW:89.1362
1-Nitropropane Catalog No.:AA003EHP CAS No.:108-03-2 MDL No.:MFCD00007407 MF:C3H7NO2 MW:89.0932	1,3-Dimethylbutylamine Catalog No.:AA003DHM CAS No.:108-09-8 MDL No.:MFCD00008088 MF:C6H15N MW:101.1900