Synthesis of stable-isotope-labeled N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide and N-(3-dimethylaminopropyl)-N′-ethylurea

Article abstract of DOI:10.1002/jlcr.3877

N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) is a carbodiimide coupling reagent commonly used for the preparation of amides from carboxylic acids and amines. Because of initial concerns regarding the genotoxicity of EDC and its use in GMP syntheses at Bristol Myers Squibb, the quantitation of residual EDC and its by-product N-(3-dimethylaminopropyl)-N′-ethylurea (EDU) by liquid chromatography–mass spectrometry (LCMS) impurity analysis was required. These analyses required the use of stable-isotope-labeled EDC and EDU to serve as internal standards. To meet this need, stable-isotope-labeled EDC 9 and EDU 10 were prepared from [1,2-¹³C₂] ethylene glycol and [¹³C,¹⁵N] potassium cyanide in overall yields of 6% and 8%, respectively.

Full text of DOI:10.1002/jlcr.3877

Received: 2 June 2020
DOI: 10.1002/jlcr.3877
Revised: 11 August 2020
Accepted: 17 August 2020
R E S E A R C H A R T I C L E
Synthesis of stable-isotope-labeled
N-(3-dimethylaminopropyl)-N0-ethylcarbodiimide and
N-(3-dimethylaminopropyl)-N0-ethylurea
Kai Cao
| John A. Brailsford | Samuel J. Bonacorsi Jr
Discovery Chemistry Platforms-
Radiochemistry, Bristol Myers Squibb
Research and Early Development,
Princeton, New Jersey, USA
Summary
N-(3-Dimethylaminopropyl)-N0-ethylcarbodiimide (EDC) is a carbodiimide
coupling reagent commonly used for the preparation of amides from carboxylic
acids and amines. Because of initial concerns regarding the genotoxicity of
EDC and its use in GMP syntheses at Bristol Myers Squibb, the quantitation
of residual EDC and its by-product N-(3-dimethylaminopropyl)-N0-ethylurea
(EDU) by liquid chromatography–mass spectrometry (LCMS) impurity analysis
was required. These analyses required the use of stable-isotope-labeled EDC
and EDU to serve as internal standards. To meet this need, stable-isotope-
labeled EDC 9 and EDU 10 were prepared from [1,2-13C2] ethylene glycol and
[13C,15N] potassium cyanide in overall yields of 6% and 8%, respectively.
Correspondence
Kai Cao, Discovery Chemistry Platforms-
Radiochemistry, Bristol Myers Squibb
Research and Early Development,
Princeton, NJ 08543, USA.
Email: kai.cao@bms.com
K E Y W O R D S
EDC, EDU, labeling, stable isotope
1 | INTRODUCTION
central carbon of the carbodiimide. In this process,
the hydroxyl group is essentially converted to a stronger
Amide bond formation reactions are one of the most
common reaction types in pharmaceutical chemistry.
A 2011 analysis of publications from the medicinal
chemistry departments of AstraZeneca, GlaxoSmithKline,
and Pfizer revealed that amide bond formation reactions
accounted for 16% of the reactions in the dataset.1 The
classic method for amide bond formation involves the
condensation of carboxylic acids and amines mediated by
a stoichiometric coupling reagent. These coupling agents
were the subject of an extensive review.2
The role of the coupling agent is to convert the
carboxylic acid into a more reactive ester intermediate.
The reactive ester is then attacked by the amine to generate
the amide or an additive such as 1-hydroxybenzotriazole
(HOBt) that improves the reaction efficiency. Carbodiimides
are often selected to serve as the coupling reagent for
amide bond formation. The carboxylic acid is activated
for substitution when the oxygen of the acid attacks the
leaving group that is ultimately expelled by a nucleophile
to generate the amide and a urea byproduct.
Among the carbodiimides available, N-(3-dimethyl-
aminopropyl)-N0-ethylcarbodiimide (EDC) is commonly
used because it is available as an HCl salt, is easy to
handle, and the urea by-product, N-(3-dimethylamino-
propyl)-N0-ethylurea (EDU), is soluble in water and can
easily be removed.3 At the time of this work, EDC was
considered to be potentially genotoxic; however, later
studies determined that EDC is not genotoxic.4 in vitro
Ames bacterial mutagenicity tests indicated EDC is
genotoxic, but the reagent is not genotoxic in vivo when
administered to rats orally. When administered orally,
EDC is hydrolyzed to EDU, which is not genotoxic.
EDC has been used in the synthesis of several
compounds under clinical development at Bristol Myers
Squibb. Because of prior concerns about potential
genotoxicity, quantitation of residual EDC and EDU in
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J Label Compd Radiopharm. 2020;63:526–530.

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SCHEME 1 Synthesis of [1,2,3-13C3]
3-dimethyl [15N]aminopropylamine (7)
SCHEME 2 Synthesis of N-([1,2,3-13C3]
3-dimethyl[15N]aminopropyl)-N0-
ethylcarbodiimide (9, EDC)
active pharmaceutical ingredients (APIs) using liquid
chromatography–mass spectrometry (LCMS) impurity
analysis was needed. The analyses utilized stable-isotope-
labeled internal standards of both EDC and EDU. The
syntheses of these labeled compounds are described
below.
SCHEME 3 Synthesis of 1-ethyl-3([1,2 3-13C3]3-dimethyl[15N]
aminopropyl)urea (10, EDU)
2 | RESULTS AND DISCUSSION
ethyl isothiocyanate in chloroform provided thiourea 8 in
quantitative yield (Scheme 2). Thiourea 8 was subjected
to dehydrosulfurization using mercury oxide red in
refluxing acetone, followed by microdistillation to give
the desired N-([1,2,3-13C3] 3-dimethyl[15N]aminopropyl)-
N0-ethylcarbodiimide (9, EDC) in 32% yield, which
was used in a free base form as an internal standard to
quantify residual EDC in APIs.
The synthetic strategy involved preparing compound 7,
a labeled diamine intermediate that can be elaborated
to either EDC or EDU, from commercially available
[1,2-13C2] ethylene glycol 1 (Scheme 1). The first steps
of the synthesis were based on the known synthesis of
[D6] 3-dimethylaminopropyl alcohol.5 Compound 1 was
heated with phosphorous tribromide to give bromoethanol
2 in 63% yield. Compound 2 was reacted with [13C15N]
potassium cyanide to yield [13C315N] ethylene cyanohydrin
(3). The nitrile of compound 3 was reduced to the amine
using lithium aluminum hydride to yield hydroxylamine
4. An initial attempt to purify compound 4 via vacuum
distillation was not successful mainly because of material
loss from vacuum distillation on a small scale. To limit
material loss, compound 4 was carried forward to the
next step as a crude product. Methylation of compound
4 with formaldehyde and formic acid followed by Vigreux
distillation yielded compound 5 containing residual diethyl
ether. Mitsunobu reaction with phthalimide was followed
by removal of the phthaloyl group with hydrazine to yield
compound 7. Compound 7 was isolated via Vigreux
distillation and contained residual diethyl ether.
The synthesis of 1-ethyl-3([1,2 3-13C3] 3-dimethyl[15N]
aminopropyl)urea (10, EDU) was accomplished by reacting
[1,2,3-13C3] 3-dimethyl [15N]aminopropylamine (7) with
ethyl isocyanate in chloroform followed by reverse-phase
preparative high-performance liquid chromatography
(HPLC) (Scheme 3).
3 | CONCLUSION
In order to quantify the amount of residual EDC and EDU
in clinical APIs, stable-isotope-labeled EDC (9) and EDU
(10) were synthesized. The labeled starting materials were
[13C2] ethylene glycol and [13C,15N] potassium cyanide.
The labeled compounds were prepared in 6% overall yield
for [13C3,15N] EDC (9) and 8% yield for [13C3,15N] EDU
(10). One of the primary challenges of these syntheses was
the volatile nature of the synthetic intermediates. This
Following the work of Pouyani et al.,6 the reaction of
[1,2,3-13C3] 3-dimethyl [15N]aminopropylamine (7) with

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CAO ET AL.
challenge was overcome by a combination of telescoping
one intermediate, using Vigreux distillation, and handling
the compounds as concentrated solutions in diethyl
ether where needed. Ultimately, the synthesis successfully
delivered stable labeled standards of EDC and EDU that
were critical for the quantitation of these impurities in
clinical samples.
was heated at 80ꢀC for 6 h then cooled in an ice bath and
filtered. The filtrate was concentrated under reduced
pressure at 40ꢀC. The resulting solution was neutralized
with 1 N HCl and diluted with acetone. The resulting
precipitate was removed by filtration and washed with
acetone. The filtrate and acetone wash were pooled and
concentrated under reduced pressure at 40ꢀC. The residue
was then vacuum distilled at 83ꢀC–85ꢀC/1.5 mmHg to yield
1
[1,2-13C2] ethylene cyanohydrin (3) (2.95 g, 80% yield). H
4 | EXPERIMENTAL
4.1 | General
NMR (400 MHz, CD3CN) δ 3.69 (dddd, J = 146.1 Hz,
12.6 Hz, 6.3 Hz, 1.7 Hz, 2H), 2.70 (m, 1H), 2.37 (m, 1H).
The 1H NMR data are consistent with those of the
unlabelled ethylene cyanohydrin: δ 3.69 (t, J = 6.1 Hz, 2H),
2.53 (t, J = 6.2 Hz, 2H). 13C NMR(100 MHz, CD3CN) δ
120.03 (ddd, J = 3.8 Hz, 17.2 Hz, 56.3 Hz), 58.22 (dd,
3.8 Hz, 36.3 Hz), 22.01 (ddd, J = 2.8 Hz, 36.3 Hz, 56.3 Hz).
All reagents and solvents used were of ACS grade
or higher. The reactions were conducted under an
atmosphere of nitrogen unless specified differently.
Ethylene-13C2 glycol, 99 atom% 13C, and potassium
cyanide-13C-15N, 99 atom% 13C & 15N were purchased from
Isotec, Inc., Miamisburg, OH. LCMS data were obtained on
a Thermo XLQ 2.0 Mass Spectrometer System with
4.1.3 | [1,2,3-13C3] 3-[15N]
Aminopropanol (4)
1
electrospray ionization. H NMR spectra were recorded on
a Bruker 400 MHz Avance II NMR spectrometer and 13C
NMR on a Bruker Avance II 300 MHz spectrometer with
Ultrashield™ magnet. Preparative HPLC was performed on
a Varian HPLC system with two PrepStar 218 pumps and
ProStar 320 variable UV detector. Preparative HPLC
method: Phenomenex LUNA C18, 5 μm, 21.2 × 250 mm,
UV detection at 220 nm, flow rate 20 ml/min. Mobile
phase A: 10 mM NH4HCO3, mobile phase B: acetonitrile.
Gradient: 15%–50% B over 10 min.
[1,2-13C2]Ethylene cyanohydrin (3) (2.95 g, 39.3 mmol) in
THF (60 ml) was cooled to −20ꢀC. Lithium aluminum
hydride (1 M in THF) was added dropwise to the mixture.
Following lithium aluminum hydride addition, the
reaction mixture was warmed to room temperature and
then heated at reflux for 8 h. The mixture was cooled to
room temperature and then quenched by the sequential
addition of water (3 ml), 15% NaOH (3 ml), and water
(9 ml). During the reaction quench, a solid formed. The
solid was removed by filtration and washed with THF
(3 × 10 ml). The filtrate and THF wash were combined
and concentrated under reduced pressure in a rotary
evaporator (stop with about 10 ml left). The crude
product was used without further purification in the
4.1.1 | [1,2-13C2]2-Bromoethanol (2)
To neat [1, 2-13C2]ethylene glycol 1 (5 g, 78 mmol)
was added phosphorous tribromide (2.43 ml, 25.8 mmol).
The mixture was then heated to 90ꢀC for 6 h. Vacuum
distillation through a 200 Vigreux column at 65ꢀC–
70ꢀC/10 mmHg yielded [1,2-13C2]2-bromoethanol (2)
(6.2 g, 63% yield). 1H NMR (400 MHz, CD3CN) δ 3.95 (m,
1
subsequent reaction. H NMR (400 MHz, CD3CN) δ 3.61
(dddd, J = 46.2 Hz, 2.4 Hz, 5.8 Hz, 11.4 Hz, 1H), 2.89 (m,
1
1H), 2.62 (m, 1H), 1.68 (m, 1H), 1.43 (m, 1H). H NMR
data are consistent with unlabelled 3-aminopropanol: δ
3.61 (t, J = 5.9 Hz, 2H), 2.76 (t, J = 6.4 Hz, 2H), 1.56 (tt,
J = 6.4, 5.9 Hz, 2H). 13C NMR (100 MHz, CD3CN) δ 62.47
(d, J = 36.3 Hz), 41.28 (dd, J = 36.2 Hz, 3.8 Hz), 35.95 (t,
J = 36.7 Hz). MS (ES+) m/z: 79.92 [M + H]+.
1
1H), 3.65 (m, 1H), 3.59 (m, 1H), 3.28 (m, 1H). The H
NMR data are consistent with those of the authentic
2-bromoethanol: δ 3.77 (t, J = 5.9 Hz, 2H), 3.47 (t,
J = 5.8 Hz, 2H). 13C NMR (100 MHz, CD3CN) δ 63.72,
63.42, 36.65, 36.34.
4.1.4 | [1,2,3-13C3]3-Dimethyl[15N]
aminopropanol (5)
4.1.2 | [13C3,15N]Ethylene cyanohydrin (3)
[1,2,3-13C3]3-[15N]Aminopropanol (4) from the previous
experiment was dissolved in formic acid (11.2 ml), cooled
in ice-water. Formaldehyde solution (37%, 11.2 ml) was
added, and the reaction mixture was heated under reflux
for 12 h. Thirty-seven percent aqueous hydrochloric acid
To a solution of [1,2-13C2]2-bromoethanol (2) (6.2 g,
49 mmol) in ethanol (16 ml) was added potassium
cyanide-13C-15N (3.29 g, 49 mmol) in water (4.8 ml).
Upon addition, the solution became turbid. The mixture

CAO ET AL.
529
(10 ml) was added to the reaction mixture, which was
then evaporated to dryness under reduced pressure.
Excess 50% aq. NaOH solution was added to the residue,
and the product was extracted with diethyl ether
(4 × 20 ml). The ether solution was dried over Na2SO4,
filtered, and distilled with a 200 Vigreux column at
atmospheric pressure at 58ꢀC. The distillation was stopped
with about 8 ml collected in the flask. The distilled
product (5.2 g) was used without further purification in
the subsequent reaction. 1H NMR showed a mixture of the
desired product and diethyl ether with a molar ratio of
1.98:1 (calculated 74% purity, 91% yield from compound
added hydrazine monohydrate (3.61 ml, 74.5 mmol). The
mixture was stirred at 80ꢀC for 12 h. The phthalimide
cleavage by-product precipitated from solution during the
reaction and was filtered. After drying, the isolated solid
weighed 0.91 g, indicating that approximately 0.6 g of the
desired amine was formed. To the ethanol filtrate was
added 1 N aq. hydrochloric acid and stirred for 5 min. The
solvent was then evaporated under reduced pressure to
dryness. Excess 50% aqueous NaOH (10 ml) was added
with cooling, and the mixture was extracted with diethyl
ether (4 × 20 ml). The ether extracts were dried over
anhydrous Na2SO4 and filtered. The ether solution was
distilled with a 200 Vigreux column at atmospheric pressure
and heating at 58ꢀC to a volume of 2–3 ml to yield
compound 7 as a solution in diethyl ether. The mass of
the product solution was 1.51 g. Based on 1H NMR
integration, the molar ratio of product amine versus ether
is 1: 4.1, 25.8% amine by weight. The yield of compound
7 was therefore calculated to be 0.39 g (49% yield). The
product solution was used without further purification.
1H NMR (400 MHz, CD3OD) δ 2.84 (m, 1H), 2.51–2.59
(m, 2H), 2.30 (dd, J = 5.0 Hz, 6H), 2.27 (m, 1H), 1.83 (m,
3). 1H NMR (400 MHz, CDCl3)
δ 3.82 (dddd,
J = 41.5 Hz,10.9 Hz, 6.0 Hz, 2.1 Hz, 2H), 2.69 (m, 1H),
2.42 (m, 1H), 2.28 (d, J = 5.3 Hz, 6H),1.83 (m, 1H), 1.58
(m, 1H). 1H NMR data are consistent with unlabelled
3-dimethylaminopropanol: δ 3.81 (t, 5.3 Hz, 2H), 2.54 (t,
J = 5.9 Hz, 2H), 2.27 (s, 6H), 1.70 (tt, J = 6.0 Hz, 5.5 Hz,
2H). 13C NMR(400 MHz, CDCl3) δ 64.71 (dd, J = 35.3 Hz,
1.9 Hz), 60.17 (ddd, J = 38.2 Hz, 2.8 Hz, 2.9 Hz), 27.89 (t,
J = 37.2 Hz). MS (ES+) m/z: 108.00 [M + H]+.
1
4.1.5 | 2-([1,2,3-13C3]3-Dimethyl[15N]
aminopropyl)isoindoline-1,3-dione (6)
1H), 1.57 (m, 1H). The H NMR data are consistent with
those of the unlabelled 3-dimethyl aminopropylamine: δ
2.65 (t, J = 7.2 Hz, 2H), 2.36 (t, J = 7.7 Hz, 2H), 2.24 (s,
6H), 1.65 (m, 2H). 13C NMR (400 MHz, CD3OD) δ 58.45
(dd, J = 3.8 Hz, 38.2 Hz), 40.97 (dd, J = 1.9 Hz, 36.2 Hz),
31.44 (ddd, J = 1.9 Hz, 36.3 Hz, 37.3 Hz).
To an ice-cold mixture of [1,2,3-13C3]3-dimethyl[15N]
aminopropanol (5) (1.630 g, 11.3 mmol, 74%), phthalimide
(2.69 g, 18.30 mmol), and triphenylphosphine (4.80 g,
18.30 mmol) in tetrahydrofuran (47.2 ml) was added
diethyl azodicarboxylate (8.33 ml, 18.30 mmol) (40% in
toluene) over 10 min. The reaction was slowly brought to
room temperature and stirred overnight. The solvent was
evaporated under reduced pressure, and the crude product
was purified by flash chromatography with ethyl acetate
and hexanes to yield the desired product 6 (2.2 g, 83%
4.1.7 | N-([1,2,3-13C3]3-Dimethyl[15N]
aminopropyl)-N0-ethylcarbodiimide (9)
An ether solution of [1,2,3-13C3]3-dimethyl[15N]
aminopropylamine (7) (4.3 g, 21.4% amine by mass,
0.91 g amine, 8.57 mmol) and ethyl isothiocyanate in
chloroform (5 ml) were stirred at room temperature
overnight under Ar. The solvent was evaporated under a
gentle stream of nitrogen to yield compound 8, which
was not purified. The crude material was dissolved in
acetone (11.4 ml), mercury (II) oxide red (2.04 g,
9.43 mmol) was added to the solution, and the mixture
was heated at 80ꢀC for 3 h. The bright orange suspension
turned black during the course of the reaction, indicating
the formation of HgS. The reaction was filtered through
Celite, concentrated, and dissolved in acetone. The acetone
solution was dried with anhydrous Na2SO4, filtered,
and transferred to a microdistillation apparatus. Vacuum
distillation at 0.6 mmHg/55ꢀC afforded compound
9 (0.44 g, 32% yield) as a colorless liquid. 1H NMR
(400 MHz, CD3OD) δ 3.40 (m, 1H), 3.23 (dq, J = 1.4 Hz,
7.3 Hz, 2H), 3.12 (m, 1H), 2.51 (m, 1H), 2.28 (m, 1H), 2.25
(d, J = 4.7 Hz, 6H), 1.15 (m, 1H), 1.61 (m, 1H), 1.22 (t,
7.2 Hz). 1H NMR data are consistent with unlabeled
1
yield) as a white solid. H NMR (400 MHz, CDCl3) δ 7.84
(dd, J = 3.0 Hz, 5.5 Hz, 2H), 7.71 (dd, J = 3.0 Hz, 5.6 Hz,
2H), 3.74 (dddd, J = 40.2 Hz, 3.6 Hz, 7.0 Hz, 10.6 Hz, 2H),
2.35 (dddd, J = 31.7 Hz, 4.2 Hz, 7.5 Hz, 11.1 Hz, 2H),
2.21 (d, J = 5.2 Hz, 6H), 1.97 (m, 1H), 1.72 (m, 1H).
1H NMR data are consistent with unlabelled 2-(3-dimethyl
aminopropyl)isoindoline-1,3-dione: δ 7.85 (dd, J = 3.0 Hz,
5.5 Hz, 2H), 7.71 (dd, J = 3.1 Hz, 5.3 Hz, 2H), 3.75 (t,
J = 7.3 Hz, 2H), 2.35 (t, J = 7.3 Hz, 2H), 2.22 (s, 6H), 1.85
(tt, J = 7.5 Hz, 7.5 Hz, 2H). 13C NMR(400 MHz, CDCl3) δ
57.02 (dd, J = 3.8 Hz, 38.1 Hz), 36.33 (dd, J = 36.3 Hz,
1.9 Hz), 26.64 (ddd, J = 36.9 Hz, 39.3 Hz, 2.4 Hz).
4.1.6 | [1,2,3-13C3]3-Dimethyl[15N]
aminopropylamine (7)
To 2-([1,2,3-13C3]3-dimethyl [15N]aminopropyl)-isoindoline-
1,3-dione (6) (2.2 g, 7.45 mmol) in ethanol (143 ml) was

530
CAO ET AL.
N-(3-dimethylaminopropyl)-N0-ethylcarbodiimide: δ 3.24-3.31
(m, 4H), 2.43 (t, J = 7.7 Hz, 2H), 2.28 (s, 6H), 1.77 (m, 2H),
1.25 (t, J = 7.3 Hz, 3H). 13C NMR (400 MHz, CD3OD) δ
58.06 (dd, J = 38. 1 Hz, 3.8 Hz), 45.86 (dd, J = 37.2 Hz,
2.9 Hz), 30.11 (t, J = 37.2 Hz). MS (ES+) m/z:
160 [M + H]+, 178 [M + NH4]+. Isotopic distribution,
M + 0(156): 0.02%, M + 1(157): 0.02%, M + 2(158): 0.12%,
M + 3(159): 2.0%, M + 4(160): 98.0%.
ACKNOWLEDGEMENTS
The authors thank the members of the Bristol-Myers
Squibb Radiochemistry Group for helpful discussions
and suggestions.
ORCID
Kai Cao https://orcid.org/0000-0002-9229-1508
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To
a
solution of [1,2,3-13C3]3-dimethyl-[15N]amino-
propylamine (7) (0.39 g, 25.8%, 0.94 mmol) in chloroform
(1 ml) was added ethyl isocyanate (67 mg, 0.94 mmol).
The mixture was stirred overnight, and the solvent
was evaporated under a steady stream of nitrogen. The
crude material was purified by preparative HPLC. Column:
Phenomenex LUNA C18 5 μm, 21.2 mm × 250 mm,
220 nm, 20 ml/min, solvent A: 10mM NH4HCO3, solvent
B: acetonitrile, 15%–50% B over 10 min. The collected
fractions were checked by LCMS to identify the fractions
containing the desired product. The desired product could
not be readily detected by UV on the HPLC chromatogram.
The product was found in fractions collected between
2 and 7 min. The pooled fractions were evaporated under
reduced pressure and then dried under high vacuum to
yield compound 10 as a colorless oil (75 mg, 43% yield).
1H NMR (400 MHz, CD3OD) δ 3.27 (m, 1H), 3.13 (q,
J = 7.2 Hz, 2H), 2.98 (m, 1H), 2.51 (m, 1H), 2.27 (d,
J = 4.7 Hz, 6H), 2.24 (m, 1H), 1.79 (m, 1H), 1.53 (m, 1H),
1.09 (t, J = 7.2 Hz). 13C NMR (400 MHz, CD3OD) δ 58.19
(dd, J = 4.3 Hz, 37.7 Hz), 39.29 (dd, J = 1.9 Hz, 37.2 Hz),
29.12 (t, J = 37.2 Hz). MS (ES+) m/z: 178 [M + H]+. Isoto-
pic distribution, M + 0(174): <0.01%, M + 1(175): 0.01%,
M + 2(176): 0.15%, M + 3(177): 1.6%, M + 4(178): 98.3%.
How to cite this article: Cao K, Brailsford JA,
Bonacorsi SJ Jr. Synthesis of stable-isotope-labeled
N-(3-dimethylaminopropyl)-N0-ethylcarbodiimide
and N-(3-dimethylaminopropyl)-N0-ethylurea. J
Label Compd Radiopharm. 2020;63:526–530.
https://doi.org/10.1002/jlcr.3877