Synthesis and characterization of n-alkylamino derivatives of vitamin K3: Molecular structure of 2-propylamino-3-methyl-1,4-naphthoquinone and antibacterial activities

Article abstract of DOI:10.1016/j.molstruc.2015.01.029

We would like to introduce eight analogues of n-alkylamino derivatives of vitamin K3 (2-methyl-1,4-naphthoquinone) viz, 2-(n-alkylamino)-3-methyl-1,4-naphthoquinone (where n-alkyl is methyl; LM-1, ethyl; LM-2, propyl; LM-3, butyl; LM-4, pentyl; LM-5, hexyl; LM-6, heptyl; LM-7, octyl; LM-8). All the above analogues have been successfully synthesized from vitamin K3 and characterized using different analytical techniques. Furthermore, in order to understand the mechanistic aspects of formation of LM-1 to LM-8 compounds, we could propose the mechanism. The FT-IR analysis of LM-1 to LM-8 indicate the presence of characteristic band of NH group ～3287-3364 cm^-1, the variation was attributed to extensive intramolecular hydrogen bonding interaction. The molecular structure of LM-3 compound has been confirmed by single crystal X-ray diffraction analysis. LM-3 compound crystallises in triclinic space group P1. There were four independent molecules in asymmetric unit cell and their molecular interactions observed via NH.

Full text of DOI:10.1016/j.molstruc.2015.01.029

Journal of Molecular Structure 1086 (2015) 179–189
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and characterization of n-alkylamino derivatives of vitamin
K3: Molecular structure of 2-propylamino-3-methyl-1,4-
naphthoquinone and antibacterial activities
Dattatray Chadar a, Maria Camilles a, Rishikesh Patil a, Ayesha Khan a, Thomas Weyhermüller b,
Sunita Salunke-Gawali a,
⇑
a Department of Chemistry, Savitribai Phule Pune University, Pune 411007, India
b MPI für Chemische Energiekonversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
First eight n-alkylamino derivatives of
vitamin K3 were synthesized.
There were four molecules in
asymmetric unit cell of propyl
derivative.
No molecular interaction between
molecules I and II similarly III and IV.
Molecules I, III and II, IV showed
III
No interaction
π−π
I
II
π−π
I
C1-C41, C1-C42, C2-C42, C9-C43,
C10-C43
C21-C62, C22-C61, C23-C70,
C30-C63
II
N-H∙∙∙O
C-H...
O
C-H...
O
III
IV
methyl and benzenoid hydrogens
H7, H48, H33B
methyl and benzenoid hydrogens
H28,H67,H68
ꢀ
ꢀ
No interaction
IV
LM-1
LM-3
CAHꢁ ꢁ ꢁO and
p–p stacking
interactions.
ꢀ
All compounds are active against
Pseudomonas aeruginosa and
Staphylococcus aureus.
a r t i c l e i n f o
a b s t r a c t
Article history:
We would like to introduce eight analogues of n-alkylamino derivatives of vitamin K3 (2-methyl-1,4-
naphthoquinone) viz, 2-(n-alkylamino)-3-methyl-1,4-naphthoquinone (where n-alkyl is methyl; LM-1,
ethyl; LM-2, propyl; LM-3, butyl; LM-4, pentyl; LM-5, hexyl; LM-6, heptyl; LM-7, octyl; LM-8). All the
above analogues have been successfully synthesized from vitamin K3 and characterized using different
analytical techniques. Furthermore, in order to understand the mechanistic aspects of formation of
LM-1 to LM-8 compounds, we could propose the mechanism. The FT-IR analysis of LM-1 to LM-8 indicate
the presence of characteristic band of NAH group ꢂ3287–3364 cmꢃ1, the variation was attributed to
extensive intramolecular hydrogen bonding interaction. The molecular structure of LM-3 compound
has been confirmed by single crystal X-ray diffraction analysis. LM-3 compound crystallises in triclinic
space group P1. There were four independent molecules in asymmetric unit cell and their molecular
Received 20 October 2014
Received in revised form 14 January 2015
Accepted 15 January 2015
Available online 27 January 2015
Keywords:
Menadione
Vitamin K3
Naphthoquinone
p–p stacking
interactions observed via NAHꢁ ꢁ ꢁO, CAHꢁ ꢁ ꢁO and
p–p stacking of quinonoid rings. Pharmacological
potential of all compounds has been evaluated in terms of their antibacterial activities against Pseudomo-
Hydrogen bonding
Michael addition
nas aeruginosa and Staphylococcus aureus. All the compounds were active against both the strains while
LM-2 was found to be more effective with a minimum inhibition concentration of 0.3125
0.156 g/mL respectively.
lg/mL and
l
Ó 2015 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +91 2025601397x531; fax: +91 2025693981.
E-mail address: sunitas@chem.unipune.ac.in (S. Salunke-Gawali).
http://dx.doi.org/10.1016/j.molstruc.2015.01.029
0022-2860/Ó 2015 Elsevier B.V. All rights reserved.

180
D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
thoquinones by single crystal X-ray diffraction and to correlate
Introduction
their structural features with the biological activity. In the present
investigation, we have reported the detailed synthesis and charac-
terization of n-alkylamino derivatives of vitamin K3 (Scheme 1). As
there is great pharmacological potential for such compounds [8]
more systematic studies have been made with respect to charac-
terization of these derivatives in the present investigation. The
antibacterial activities of these compounds were also evaluated
against two bacterial strains namely viz., Staphylococcus aureus
and Pseudomonas aeruginosa.
Vitamin K is a group of structurally similar and fat-soluble vita-
mins that are needed for the post-translational modification of cer-
tain proteins required for blood coagulation as well as in metabolic
pathways in bone and other tissues. Vitamin K is found chiefly in
green leafy vegetables such as dandelion greens, spinach, swiss
chard and Brassica (e.g. Cabbage, cauliflower, broccoli and brussel
sprouts). Some fruits, such as avocado, kiwifruit and grapes are also
high in vitamin K. Colonic bacteria synthesize a significant portion
of vitamin K that needs human. The potential health problems that
can be associated with vitamin K deficiency include arterial calci-
fication, cardiovascular disease and varicose veins, osteoporosis,
prostate cancer, lung cancer, liver cancer and leukemia, brain
health problems, including dementia, tooth decay and infectious
diseases like pneumonia.
Experimental section
General materials and methods
The materials used viz., 2-methyl-1,4-naphthoquinone, methyl
amine solution (40%), ethyl amine solution (70%), propyl, butyl,
All form of vitamin K share a common scaffold viz. 1,4-naphtho-
quinone ring, however differ in the C(3) side chain. There are three
major types of vitamin K, phylloquinone (VK1), menaquinone
(VK2) and menadione (VK3). VK1 and VK2 are the natural com-
pounds; the most common form of VK2 in human is menaquin-
one-4 (MK-4) [1]. VK3 (2-methyl-1,4-naphthoquinone) is
considered as the synthetic analogue. Davidson et al. [2–4] have
found that dietary VK1 can be cleaved to form VK3 by bacteria
present in the intestine. It is also an intermediate metabolite in
the conversion of VK1 to MK4 [5] and plays important role in blood
coagulation as a cofactor for the synthesis of clotting factors in liver
and in bone mineralisation [4,6].
Biological activity of quinones has been related to their capacity
to accept one or two electrons to forms the corresponding radical
anion or radical dianion. The electron uptake capacity of a given
quinone can be modified by directly adding substituent’s to the
quinone structure. Structural aspects are very important factor as
for as the biological activity of the synthetic molecules are con-
cerned. We have described in our series of reports on the n-alky-
laminno derivatives of naphthoquinones, that these molecules
could provide facile sites for molecular interaction to biomolecules.
pentyl, hexyl, heptyl and octyl amine were purchased from
Sigma–Aldrich and used as received. Analytical grade solvents used
such as dichloromethane, toluene, methanol were purchased from
Merck Chemicals. Solvents were distilled by standard methods [9]
and dried wherever necessary. FT-IR spectra were recorded
between 4000 and 400 cmꢃ1 as KBr pellets on SHIMADZU FT
8400 Spectrophotometer (Fig. S1a–h in ESI ). Melting points of
LM-1 to LM-8 were determined using (Make-METTLER) and were
corrected using DSC (Differential Scanning Calorimetry) technique
(Make-TA Q2000) (Fig. S2a–h in ESI ). 1H, 13C and DEPT NMR of
compounds were recorded (Fig. S3a–h and Table S1 in ESI ) in
DMSO-d6, on Varian 500 MHz NMR instrument. TMS (tetramethyl-
silane) was used as the reference. Elemental analysis was per-
formed on Thermo Finnigan EA 1112 Flash series Elemental
Analyzer and on Elementar Vario EL III. Mass of LM-1 to LM-8
was determined by GC–MS 2010-eV (Make SHIMADZU).
Synthesis
Synthesis of n-alkylamino derivatives of vitamin K3
These interactions could include hydrogen bonding,
p–p stacking
interactions [7]. Our main interest in the resent years is to study
the molecular interactions of n-alkylaminno derivatives of naph-
1 g of vitamin K3 (5.80 mM) was taken in a two necked round
bottom flask. About 25 ml dichloromethane was added to it just
so that it dissolves. After stirring the solution on a magnetic stirrer
O
Table 1
Details of concentration of primary amines used in synthesis of LM-1 to LM-8.
8
9
1
NH
Comp.
Vitamin K3
weight (g)
Primary amine
(% soln)
Density
g/cm3
Volume
mL
Yield
(%)
7
6
CH2R
2
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Methyl (40%)
Ethyl (70%)
Propyl (99%)
Butyl (99%)
Pentyl (99%)
Hexyl (99%)
Heptyl (99%)
Octyl (99%)
0.893
0.800
0.717
0.740
0.752
0.766
0.777
0.782
0.504
0.543
0.482
0.571
0.772
0.772
0.861
0.950
42.40
40.00
38.72
37.31
39.66
32.33
34.50
34.28
CH3
3
10
4
5
O
Scheme 1. Molecular formula of LM-1 to LM-8. Where, LM-1: R@H; LM-2: R@CH3;
LM-3:R@C2H5, LM-4: R@C3H7, LM-5: R@C4H9; LM-6: R@C5H11; LM-7: R@C6H13; LM-
8: R@C7H15
.

D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
181
for about 15 min, calculated amount of primary amine solution
(Table 1) (methylamine, ethylamine, propylamine, butylamine,
amylamine, hexylamine, heptylamine, octylamine) was added to
it. The reaction was kept for 24 h with constant stirring at room
temperature ꢂ28 °C. During this time the progress of the reaction
was monitored using thin layer chromatography. After 24 h the
mixture was transferred to a beaker and kept for another 24 h
for the solvent to evaporate. The solid crude product was obtained
by evaporation. The crude product was purified by column chro-
matography using toluene: methanol (9:1) as eluent. Red colour
needles of all the derivatives were obtained by the slow evapora-
tion of eluent.
561, 507, 451, 418. 1H NMR (500 MHz, DMSO-d6, d/ppm): 0.83 (t,
3H, J = 7.00 Hz), 1.25 (m, 2H, J = 7.25 Hz)), 1.55 (p, 2H,
J = 7.25 Hz), 3.35 (q, 2H, J = 7.00 Hz), 2.07 (s, 3H), 6.59 (br. 1H),
7.66 (t, 1H, J = 7.50 Hz), 7.75 (t, 1H, J = 7.75 Hz), 7.84 (d, 1H,
J = 7.25 Hz), 7.99 (d, 1H, J = 7.75 Hz). UV–Vis (kmax/nm, DMSO):
281, 342, 487. GC–MS (EI); m/z: 285 (M+ + H).
Characterization of 2-octylamino-3-methyl-1,4-naphthoquinone (LM-
8)
Red crystal, Yield: 0.593 g (34.28%). M. P. 60.96 °C. Anal. data
calcd. for C19H25NO2: C, 76.27; H, 8.42; N, 4.68. Found: C, 76.28;
H, 7.77; N, 4.83. FT-IR (KBr, m
max/cmꢃ1): 3282, 3068, 2958, 2922,
Characterization of 2-ethylamino-3-methyl-1,4-naphthoquinone (LM-
2)
2853, 1668, 1618, 1600, 1566, 1505, 1457, 1366, 1339, 1300,
1277, 1233, 1179, 1157, 1124, 1107, 1083, 1063, 1028, 969, 952,
896, 813, 797, 753, 724, 683, 667, 652, 623, 561, 532, 509, 470,
453, 434, 411. 1H NMR (500 MHz, DMSO-d6, d/ppm): 0.82 (t, 3H,
J = 7.00 Hz), 1.25 (m, 2H, 7.25), 3.51 (q, 2H, J = 7.80 Hz), 2.05 (s,
3H), 6.60 (br. 1H), 7.67 (t, 1H, J = 7.50 Hz), 7.76 (t, 1H,
J = 7.25 Hz), 7.86 (d, 1H, J = 7.75 Hz), 7.92 (d, 1H, J = 8.00 Hz). UV–
Vis (kmax/nm, DMSO): 280, 340, 487. GC–MS (EI); m/z: 299
(M+ + H).
Dark red crystal, Yield: 0.499 g (40.0%). M. P. 87.97 °C. Anal. data
calcd. for C13H13NO2 C, 71.63; H, 5.51; N, 6.96. Found: C, 72.29; H,
6.20; N, 6.51. FT-IR (m
max/cmꢃ1): 3285, 3182, 3068, 2966, 2926,
2870, 1670, 1602, 1566, 1510, 1452, 1344, 1280, 1228, 1184,
1150, 1080, 1051, 1028, 979, 941, 887, 862, 804, 725, 684, 630,
553, 518, 478, 435, 410. 1H NMR (500 MHz, DMSO-d6, d/ppm):
1.15 (t, 3H, J = 7.00 Hz), 3.55 (p, 2H, J = 7.00 Hz), 6.56 (br. S, 1H,
D20 ex.), 2.07 (s, 3H), 7.65 (t, 1H, J = 7.50 Hz), 7.75 (t, 1H,
J = 7.90 Hz), 7.88 (d, 1H, J = 7.80 Hz), 7.90 (d, 1H, J = 8.60 Hz). UV–
Vis (kmax/nm, DMSO): 280, 313, 486. GC–MS (m/z): 215 (M+ + H).
X-ray crystallographic data collection and refinement of the structure
Single crystals of LM-3 was coated with perfluoropolyether,
picked up with nylon loops and was mounted in the nitrogen cold
Characterization of 2-propylamino-3-methyl-1,4-naphthoquinone
(LM-3)
stream of the diffractometer. Monochromated Mo K
a radiation
(Bruker-AXS Kappa Mach3 with Incoatec Helios mirror,
k = 0.71073 Å) from a Mo-target rotating-anode X-ray source was
used for LM-3. Final cell constants were obtained from least
squares fits of several thousand strong reflections. Intensity data
were corrected for absorption using intensities of redundant reflec-
tions with the program SADABS [10]. The structures were readily
solved by direct methods and subsequent difference Fourier tech-
niques. The Siemens ShelXTL [11] software package was used for
solution and artwork of the structures, ShelXL97 [12] was used
for the refinement. All non-hydrogen atoms were anisotropically
refined and hydrogen atoms were placed at calculated positions
Red crystals, Yield: 0.515 g (38.72%). M. P. 77.19 °C. Anal. data
calcd. for C14H15NO2: C, 73.34; H, 6.59; N, 6.11. Found: C, 73.03;
H, 6.50; N, 5.64. FT-IR (KBr, m
max/cmꢃ1): 3284, 3180, 3068, 2958,
2872, 1669, 1602, 1566, 1510, 1452, 1344, 1280, 1228, 1184,
1151, 1099, 1080, 1060, 1026, 976, 896, 786, 727, 684, 630,557,
503, 451, 441. 1H NMR (500 MHz, DMSO-d6, d/ppm): 0.83 (t, 3H,
J = 7.50 Hz), 1.55 (p, 2H, J = 7.75 Hz), 3.41 (q, 2H, J = 7.20 Hz), 2.03
(s, 3H), 6.53 (br. 1H), 7.69 (t, 1H, J = 7.50 Hz), 7.80 (t, 1H,
J = 7.50 Hz), 7.84 (d, 1H, J = 7.25 Hz), 7.90 (d, 1H, J = 7.75 Hz). UV–
Vis (kmax/nm, DMSO): 281, 339, 487. GC–MS (EI); m/z: 229
(M+ + H).
Table 2
Characterization of 2-pentylamino-3-methyl-1,4-naphthoquinone
(LM-5)
Crystal data and structure refinement for LM-3.
Identification code
LM-3
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system, space group
Unit cell dimensions
C
14H15NO2
Red crystal, Yield: 0.591 g (39.66%). M. P. 83.31 °C. Anal. data
229.27
calcd. for C16H19NO2: C, 74.68; H, 7.44; N, 5.44. Found: C, 74.71;
100(2) K
0.71073 A
Triclinic, P1
a = 9.8975(6) Å
H, 7.55; N, 5.66. FT-IR (KBr, m
max/cmꢃ1): 3338, 33072, 2952, 2866,
1668, 1601, 1565, 1525, 1462, 1340, 1301, 1274, 1230, 1180,
1155, 1087, 1064, 1026, 985, 906, 840, 792, 729, 688, 636, 555,
505, 457,428. 1H NMR (500 MHz, DMSO-d6, d/ppm): 0.82 (t, 3H,
J = 7.80 Hz), 1.25 (m, 2H, J = 7.20), 1.52 (p, 2H, J = 7.20 Hz), 3.49
(q, 2H, J = 7.00 Hz), 2.08 (s, 3H), 6.53 (br. 1H), 7.64 (t, 1H,
J = 7.25 Hz), 7.74 (t, 1H, J = 7.25 Hz), 7.88 (d, 1H, J = 7.25 Hz), 7.90
(d, 1H, J = 7.80 Hz). UV–Vis; (kmax/nm, DMSO): 280, 335, 487.
GC–MS (EI); m/z: 257 (M+ + H).
a
= 97.904(4)°
b = 9.9631(6) Å b = 107.789(5)°
c = 12.7937(8) Å
4, 1.316 Mg/m3
0.088 mmꢃ1
488
c = 100.155(4)°
Z, Calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Limiting indices
Reflections collected/unique
Completeness to theta
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
0.16 ꢄ 0.16 ꢄ 0.10 mm
2.69–33.09°
ꢃ15 6 h 6 13, ꢃ15 6 k 6 15, ꢃ19 6 l 6 19
31,985/16,066 [R(int) = 0.0534]
33.09% and 99.7%
Characterization of 2-heptylamino-3-methyl-1,4-naphthoquinone
(LM-7)
0.99206 and 0.98593
Full-matrix least-squares on F2
16,066/3/633
Red crystal, Yield: 0.568 g (34.5%). M. P. 51.42 °C. Anal. data
1.070
R1 = 0.0569, wR2 = 0.1176
R1 = 0.0852, wR2 = 0.1327
Not applicable, light atom structure
0.397 and ꢃ0.330 e Åꢃ3
calcd. for C18H23NO2: C, 75.76; H, 8.12; N, 4.91. Found: C, 75.21;
H, 8.04; N, 5.21. FT-IR (KBr, m
max/cmꢃ1): 3323, 3066, 2955, 2924,
Absolute structure parameter
Largest diff. peak and hole
2856, 1668, 1599, 1564, 1510, 1460, 1334, 1300, 1278, 1230,
1180, 1153, 1085, 1030, 970, 893, 800, 767, 727, 684, 653, 623,

182
D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
and refined as riding atoms with isotropic displacement parame-
ters. Crystallographic data of the compounds are listed in Table 2.
3 and so on. The plates were further incubated at 30 °C and latter
scanned at 620 nm using a multiplate reader. The results were pre-
sented in the form of plots of absorbance Vs concentrations.
Antibacterial activity
Result and discussion
Agar disc diffusion assay
Bacterial strains P. aeruginosa (PAO-1) and S. aureus were
obtained for National Chemical Laboratory, Pune, India. Initially,
the apparatus as well as potato dextrose agar (PDA) (5.85 g in
150 ml distilled water) was sterilized by autoclaving it for
20 min. The PDA was then poured on to the petri plates and kept
for 24 h. The work was carried out in the laminar air flow (Micro-
filt) using a micropipette 200 lL of bacterial sample was spread on
to the plates evenly using a spreader. Using sterilized forceps small
sterilized discs of Whatman filter paper 1 was placed on the plate
The first eight n-alkylamino analogues of vitamin K3 has been
synthesized at room temperature (26 °C). The products were
obtained by evaporation of dark red fraction from the column. First
yellow fraction was found to be unreacted vitamin K3. A dark
brown coloured product band retained on the column, which
was inseparable by the chromatographic conditions used for sepa-
ration (9:1, toluene: methanol). The dark red coloured product was
later found to be 2-(n-alkylamino)-3-methyl-1,4-naphthoquinone
with yield of ꢂ40%, which was on the lower side when compared
to bromo chloro, hydro derivatives of 2-X-3-(n-alkylamino)-1,4-
naphthoquinone.
The mechanism for formation of n-alkylamino derivatives of
vitamin K3 is as shown in Scheme 2. PATH 1 explains the formation
of desired product 2-(n-alkylamino)-3-methyl-1,4-naphthoqui-
none, whereas PATH-2 explains formation of the by product. 2-
methyl-1,4-naphthoquinone(1), the starting material used in the
synthesis is an unsymmetrical Michael acceptor molecule, which
could undergo the Michael addition reaction with variety of
amines to gives the nucleophilic substitution reaction [13] at the
sp2 carbon atom. As a result, the compound (4) is possibly the
major product in this reaction. Mechanistically, it is predicted, that
Michael addition of primary amine (1) will lead to the generation
of an intermediate compound (3). It could be better represented
by enolisation of the compound (3) into the more stable (30) form.
equidistantly. On these discs 1
pounds LM-1 to LM-8 and vitamin K3 solutions in DMSO were
placed (Concentration of the compound = 2 mg/100 L.). DMSO
lL, 2 lL, 3 lL and 5 lL of the com-
l
was used as a control. The plates were then incubated at 30 °C
for 48 h and the zone of inhibitions were measured.
Minimum inhibitory concentration assay (MIC)
Using a multipipettor, 100
the wells of a microtitre plate. The plates and lid were labelled.
About 100
L of appropriate 2ꢄ antibiotic solutions were pipetted
into the wells in column 1. Using the multipipette set at 100 L, the
antibiotics were mixed into the wells of column 1 by sucking up
and down 6–7 times. 100 L mixtures were withdrawn from col-
lL of medium was dispensed into
l
l
l
umn 1, and added this to column 2. This made column 2 a twofold
dilution of column 1 and it was repeated from column 2 to column
Scheme 2. Probable reaction mechanism of LM-1 to LM-8.

D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
183
It could undergo oxidation under the influence of another mole of
2-methyl-1,4-naphthoquinone (1) as mentioned by Ji et al. [14].
However, the formation of product (7) is much straight forward,
wherein the direct 1,2-addition of the primary amine (I) to vitamin
K3 (1) leads to an intermediate (5) as an unstable moiety, which
immediately loses the water molecules to give the aminonaphtho-
quinone (7).
bonding especially in LM-2, LM-3 and LM-8. However, it can be
generalised that the mNAH stretch (in LM-1 to LM-8) was observed
at a higher frequency as compared to the corresponding chloro,
bromo derivatives of 2-(X)-3-(n-alkylamino)-1,4-naphthoquinone
(L-1 to L-4, L-1Br to L-4Br, and LH-1 to LH-7) [7]. The carbonyl
stretching frequency was observed at 1661 cmꢃ1 for parent
2-methyl-1,4-napthoquinone, however this frequency was shifted
to higher wave number in LM-1 to LM-8. The frequencies were
observed in the range of ꢂ1661–1669 cmꢃ1 (Fig. 1b). New band
appeared at ꢂ1734 cmꢃ1 which was also assigned to carbonyl fre-
FT-IR studies of LM-1 to LM-8
quency. mCAN frequency was observed at ꢂ1600 3 cmꢃ1
. mC@C
The band observed ꢂ3364–3282 cmꢃ1 in FT-IR spectra of LM-1
to LM-8 was assigned for mNAH stretching frequency in Fig. 1
(Table 3). The minor variation in mNAH frequency suggests that it
was influenced by intra as well as intermolecular hydrogen
showed (ꢂ1560 cmꢃ1) decrease in frequency to all compounds
ꢂ25 cmꢃ1 when compared with parent, vitamin K3. Paranaphtho-
quinone vibrations (
lower values than that of vitamin K3, which implies that the
m
pANQ) was observed at ꢂ1280 cmꢃ1 and are at
carbonyl oxygen are involved in hydrogen bonding.
90
1H and 13C NMR of LM-1 to LM-8
1H and 13C NMR spectra of the LM-1 to LM-8 were recorded in
DMSO-d6 solvent. In 1H NMR spectra, the terminal methyl protons
(a) shows triplet in LM-2 to LM-8, while they are observed as a
doublet in LM-1 (Scheme 3). CH2 protons (h) in LM-3 to LM-8
showed quartet while in LM-2, they are observed as pentet, CH2
protons (b) in LM-3 to LM-8 showed multiplet. The respective
CH2 protons c, d, e, f and g showed pentet, the resonance of
AN(11)AH(11) proton was observed as quartet in LM-1, whereas
they observed a triplet in LM-2 to LM-8 ꢂ d = 6.59 ppm. 13C chem-
ical shifts were assigned to all compounds and are presented in
Table 4.
75
LM
LM-1
LM-2
60
45
30
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
(a)
3600
3500
3400
3300
3200
3100
Wavenumber (cm-1)
UV–Visible spectra of LM-1 to LM-8
LM
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
Electronic spectra of all compounds are shown in Fig. 2.
ꢂ1 ꢄ 10ꢃ4 M concentration were used to record the electronic
spectra of LM-1 to LM-8 and the starting material vitamin K3.
The absorption of the visible region was observed in starting all
compounds owing to a fully conjugated cyclic dione system and
the non bonding electrons of the amino group which allows the
possibility of n–p⁄ transition in the visible region [7].
90
75
60
45
30
15
The electronic spectra of LM-1 to LM-8 showed the band in the
UV region around 291–297 nm and at 335–337 nm (p–
p⁄ elec-
tronic transition) (Fig. 2). In addition, a third lower energy transi-
tion appeared in the visible region of 477 nm. This absorption is
typical of amino substituted quinone [15]. The lower energy
absorption 477 nm was assigned, to the charge transfer (CT) tran-
sition and weak n ? p⁄ transition’s band result from the electron
donating effect of the substituted amine in LM-1 to LM-8. It is
known that full delocalization of the nitrogen lone pair requires
its orthogonality to be in the plane of naphthoquinone. Thus the
shape of the amine influences the extent of the bathochromic shift.
LM-1 to LM-8 differed in the length of the alkyl chain present on
(b)
1700
1600
1500
1400
Wavenumber (cm-1)
Fig. 1. Characteristic FT-IR frequencies of LM-1 to LM-8 (a) mNAH region, (b) mC@O
and mCAN region.
Table 3
FT-IR frequencies for vitamin K3 and LM-1 to LM-8.
Comp.
mNAH
mCAH
mC@O
mCAN
mC@C
mpANQ
LM
–
3068, 2920, 1460, 1156
3072, 3032, 1468, 1158
3182, 3068, 1452, 1150
3180, 3068, 1452, 1151
3068, 2956, 1454, 1155
2952, 2929, 1462, 1155
3066, 2953, 1459, 1153
3066, 2955, 1460, 1153
3068, 2958, 1458, 1151
1660, 1622
1667
1670
1669
1668
1668
1671
1668
1670
–
1590, 1326
1562, 1342
1510, 1344
1566, 1344
1568, 1342
1565, 1340
1565, 1340
1564, 1334
1566, 1344
1299
1292
1280
1280,
1280
1274
1276
1278
1280
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
3364
3285
3284
3323
3338
3323
3323
3282
1600
1602
1602
1599
1601
1599
1599
1601

184
D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
Scheme 3. Atom numbering scheme to assign 1H and 13C NMR spectra of LM-1 to LM-8 (letter a, b, c, d, e, f, g and h are assigned to carbon atom. In parenthesis d (doublet), m
(multiplet), p (pentet), q (quartet) and t (triplet) denotes peak obtained in 1H NMR spectra.
Table 4
13C chemical shift (d/ppm) of LM-1 to LM-8 in DMSO-d6.
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
C1
C2
C3
C4
C5
C8
C6
C7
C9
C10
C-12
f
181.53
147.56
109.89
182.22
126.89
126.23
134.53
134.22
130.71
131.96
10.44
–
181.54
146.53
110.42
182.19
125.53
125.30
134.34
132.74
130.23
131.99
10.51
–
181.63
146.71
110.67
182.26
125.36
125.61
134.43
132.78
130.26
132.43
10.61
181.45
146.50
110.49
182.09
126.67
125.48
134.53
132.10
130.12
131.92
10.52
–
181.55
146.62
110.54
182.22
125.59
125.35
134.41
132.05
130.24
132.77
10.61
–
181.82
146.90
110.83
182.49
125.85
125.62
134.67
132.17
130.51
132.31
10.63
–
181.73
146.78
110.72
182.34
125.70
125.46
134.54
132.18
130.32
132.86
10.69
–
181.56
146.65
110.59
182.24
125.59
125.35
134.78
132.05
130.26
132.78
10.63
26.10
e
d
c
g
b
h
a
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
26.14
28.44
31.26
30.66
22.08
44.52
13.99
28.67
28.62
31.20
30.58
22.08
44.41
13.93
26.06
30.95
30.60
22.05
44.68
13.87
28.35
30.33
21.86
44.39
13.90
32.65
19.28
44.03
13.60
–
23.87
46.09
11.00
40.26
16.31
32.40
3.0
unlike other n-alkylamino derivatives [7,19] and several other
derivatives of vitamin K3 [20]. Major differences were observed
to the (i) torsion angles of all four molecules, especially to the
plane of quinonoid ring and the N-alkyl groups (Table S2 in ESI )
and similarly (ii) bond angle especially \N(11)AC(12)AC(13) and
\N(31)AC(32)AC(33) are 114.3°, while \N(51)AC(52)AC(53) =
110.3° and \N(71)AC(72)AC(73) = 109.3°.
Molecules of LM-3 show intra as well as intermolecular hydro-
gen bonding (Table 5). Among four molecules of LM-3, similar ends
of pair of molecule I, IV and II, III formed dimers via NAHꢁ ꢁ ꢁO inter-
actions. However Dꢁ ꢁ ꢁA distances as well as \DAHꢁ ꢁ ꢁA varies in
these dimers (Table 5).
2.5
2.0
1.5
1.0
0.5
0.0
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
LM
300
450
600
750
Molecules I, III and II, IV showed
CAHꢁ ꢁ ꢁO interaction of benzenoid ring hydrogen’s (Fig. 4). The car-
bon atoms involved in stacking interaction of molecules I and
III are C(1)ꢁ ꢁ ꢁC(41) (3.361(3) Å), C(1)ꢁ ꢁ ꢁC(42) (3.319(3) Å),
C(2)ꢁ ꢁ ꢁC(41) (3.300(3) Å), C(9)ꢁ ꢁ ꢁC(43) (3.466(3) Å), C(10)ꢁ ꢁ ꢁC(43)
(3.362(2) Å) (1 + x,y,z), and those of molecules II and IV are
p–p stacking as well as
Wavelength (nm)
Fig. 2. UV–Visible spectra of vitamin K3 and LM-1 to LM-8 in DMSO with
concentration ꢂ1 ꢄ 10ꢃ4 M.
p–p
the amino nitrogen and, therefore, does not differ greatly in their
absorption [16–18].
C(21)ꢁ ꢁ ꢁC(62)
(3.299(3) Å),
C(22)ꢁ ꢁ ꢁC(61)
(3.299(3) Å),
C(23)ꢁ ꢁ ꢁC(70) (3.352(2) Å), C(30)ꢁ ꢁ ꢁC(63) (3.372(3) Å) (x,y,z).
Molecular interactions of each molecule of LM-3 were analyzed
in detail. Molecule I (Fig. 4a), II (Fig. 4b) and IV (Fig. 4d) were in
vicinity to four and molecule III (Fig. 4c) was in vicinity to five
Single crystal X-ray studies of LM-3 and hydrogen bonding interaction
of LM-1
Molecules of LM-3 crystallize in triclinic P1 space group. There
were four independent molecules in asymmetric unit cell. For our
convenience we named these molecules as I, II, III and IV, ORTEP
diagram of the same shown in Fig. 3 and the crystallographic data
were presented in Table 2.
neighbouring molecules via NAHꢁ ꢁ ꢁO, CAHꢁ ꢁ ꢁO and
p–p stacking
interactions. Methyl group hydrogen (H(15A), H(55A), H(35C)
and H(75C)) and benzenoid hydrogen’s (H(7), H(28), H(48), H(67)
and H(68)) were involved in CAHꢁ ꢁ ꢁO interaction. Only n-alkyl-
amino hydrogen H(33B) of molecule II showed CAHꢁ ꢁ ꢁO interac-
tion to O(41) of molecule III. When viewed down ‘b’-axis (Fig. 5)
There were minor variation in C@O, CAN bond distances of all
four molecules, however all the molecules are in oxidized form
the dimers of molecules I, IV and II, III further show p–p stacking

D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
185
III
I
II
IV
Fig. 3. Asymmetric unit of LM-3.
Table 5
Hydrogen bond geometries for LM-1 and LM-3.
0
0
0
Com
Sr. No
DAHꢁ ꢁ ꢁA
\DAHꢁ ꢁ ꢁA (°)
DAH (AÅ)
Hꢁ ꢁ ꢁA (AÅ)
Dꢁ ꢁ ꢁA (AÅ)
LM-1
1
2
3
4
5
6
7
8
N(11)AH(11)ꢁ ꢁ ꢁO(4)(i)
C(12)AH(12B)ꢁ ꢁ ꢁO(4)(i)
C(13)AH(13A)ꢁ ꢁ ꢁO(1)(ii)
C(8)AH(8)ꢁ ꢁ ꢁO(1)(i)
0.92 (2)
0.981 (1)
0.979 (1)
0.981 (2)
0.94 (3)
0.98 (3)
0.92 (3)
0.94 (3)
0.92 (3)
0.94 (3)
0.94 (3)
0.98 (3)
0.980 (2)
0.981 (2)
0.980 (2)
0.979 (2)
0.951 (2)
0.950 (2)
0.950 (2)
0.950 (4)
0.990 (2)
2.36 (2)
3.060 (1)
3.209 (2)
3.393 (2)
3.360 (2)
2.608 (2)
2.599 (2)
2.612 (3)
2.601 (3)
2.961 (2)
3.405 (2)
2.933 (3)
3.392 (3)
3.424 (3)
3.433 (2)
3.464 (2)
3.398 (3)
3.211 (3)
3.401 (3)
3.242 (3)
3.074 (3)
3.444 (2)
133.0 (2)
126.5 (1)
139.0 (1)
163.8 (8)
109.0 (2)
110.0 (2)
109.0 (2)
110.0 (2)
153.0 (2)
162.0 (2)
151.0 (2)
158.0 (2)
133.3 (1)
143.2 (1)
137.6 (1)
140.5 (1)
164.5 (1)
165.2 (1)
133.2 (1)
128.1 (1)
132.6 (1)
2.527 (1)
2.593 (1)
2.436 (1)
2.14 (3)
2.10 (3)
2.16 (3)
2.14 (3)
2.11 (3)
2.50 (3)
2.071 (3)
2.696 (3)
2.677 (2)
2.597 (1)
2.677 (1)
2.586 (2)
2.285 (2)
2.474 (3)
2.517 (3)
2.395 (2)
2.696 (2)
LM-3
N(31)AH(31)ꢁ ꢁ ꢁO(24)intra
N(51)AH(51)ꢁ ꢁ ꢁO(44)intra
N(11)AH(11)ꢁ ꢁ ꢁO(4)intra
N(71)AH(71)ꢁ ꢁ ꢁO(64)intra
N(11)AH(11)ꢁ ꢁ ꢁO(64)(iii)
N(71)AH(71)ꢁ ꢁ ꢁO(4)(iii)
N(31)AH(31)ꢁ ꢁ ꢁO(44)(iv)
N(51)AH(51)ꢁ ꢁ ꢁO(24)(iv)
C(15)AH(15A)ꢁ ꢁ ꢁO(41)(iv)
C(55)AH(55A)ꢁ ꢁ ꢁO(1)(iv)
C(35)AH(35C)ꢁ ꢁ ꢁO(61)(v)
C(75)AH(75C)ꢁ ꢁ ꢁO(21)(v)
C(7)AH(7)ꢁ ꢁ ꢁO(41)(v)
9
10
11
12
13
14
15
16
17
18
19
20
21
C(48)AH(48)ꢁ ꢁ ꢁO(1)(vi)
C(28)AH(28)ꢁ ꢁ ꢁO(61)(vii)
C(67)AH(67)ꢁ ꢁ ꢁO(21)(iv)
C(33)AH(33B)ꢁ ꢁ ꢁO(41)(v)
(i) ½ꢃx, ½ꢃy, ꢃz; (ii) 1ꢃx, y, ½ꢃz; (iii) 1 + x, ꢃ1 + y. Z; (iv) ꢃ1 + x,y,z; (v) x,y,z; (vi) x, ꢃ1 + y, ꢃ1 + z, (vii) x, 1 + y, z.
interactions. The ladders like interactions of LM-3 molecules via
stacking interactions were illustrated in Fig. 6.
The ladders were connected by a unique CAHꢁ ꢁ ꢁO interaction of
n-alkyl group of molecule II to oxygen of molecule III. There were
no interactions observed between molecules I, II and III, IV.
C(1)ꢁ ꢁ ꢁC(2) (3.429(2) Å), C(3)ꢁ ꢁ ꢁC(1) (3.398(2) Å), C(3)ꢁ ꢁ ꢁC(10)
(3.391(2) Å).
stacked molecules were also hold by CAHꢁ ꢁ ꢁO
interactions of C(2)ACH3 group. When viewed down ‘b’-axis each
(Fig. 7) Stacked polymeric chains were observed to dimeric
LM-1 molecules whereas viewed down ‘c’ axis a beautiful butterfly
NAHꢁ ꢁ ꢁO and
p–p
p–p
p–p
like architecture was observed to two pairs of
molecules (Fig. 7).
p–p stacked LM-1
Molecular interactions in LM-1
A molecule of LM-1 (CCDC No. 640771) [8a] crystallizes in
monoclinic C2/c space group and showed dimer via NAHꢁ ꢁ ꢁO and
CAHꢁ ꢁ ꢁO interactions of similar ends of oppositely orientated mol-
ecules. This interaction is commonly observed in other n-alkyl-
amino derivatives of 1,4-naphthoquinones [7]. Each LM-1
Antibacterial activity of LM-1 to LM-8
The antibacterial activity of LM-1 to LM-8 compounds along
with vitamin K3 has been evaluated against two bacterial strains
viz, S. aureus and P. aeruginosa by the agar disc diffusion assay
and minimum inhibitory concentration assay.
molecule was in vicinity to four neighbouring molecules (i)
p–p
stacked as well as CHꢁ ꢁ ꢁO interaction of C(13-H(13A)ꢁ ꢁ ꢁO(1) (1ꢃx,
y, ½ꢃz). (ii) forms dimer with oppositely oriented neighbouring
molecule by NAHꢁ ꢁ ꢁO (½ꢃx, ½ꢃy,ꢃz) interaction. (ii) Two mole-
cules with CAHꢁ ꢁ ꢁO interaction (½ꢃx, ½ꢃy, ½ꢃz).
Bacterial strain like S. aureus is one of the major resistant patho-
gens found on the mucous membrane and human skin and extre-
mely adaptable to antibiotic pressure. It was found to be resistant
against clinically used Penicillin and Methicillin drugs. While P.
aeruginosa is a highly prevalent opportunistic pathogen. It is the
most common pathogen isolated from patients who have been
p–p stacking interaction are observed to neighbouring alternat-
ing molecules of LM-1 and the carbon atoms involved were

186
D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
Fig. 4. (a) Neighbouring molecules of I, (b) neighbouring molecules of II, (c) neighbouring molecules of III and (d) neighbouring molecules of IV.
Fig. 5. Hydrogen bonding and
p
–p
stacking interactions in LM-3 down b-axis.
hospitalized longer than one week. It is a frequent cause of nosoco-
mial infections such as pneumonia, urinary tract infections and
bacteremia especially in patients with compromised host defence
mechanisms. One of the most agonizing characteristics of P. aeru-
ginosa is its low antibiotic susceptibility. This inactivity may result
from lack of prescriber knowledge of specific antimicrobial resis-
tance patterns or suboptimal dosing based on pharmacokinetic
and pharmacodynamic properties of each drug class. Hence, there
has been a need to synthesis a new class of drug against which
these pathogens that do not develop any resistance.
petriplates. The results were presented in Table 6 (Fig. S4 in ESI )
for P. aeruginosa and S. aureus (in parenthesis). It was observed that
all of the compounds showed some activity against the two bacte-
rial strains. In all the cases, there was an increase in the diameter of
the clearance zone with increase in the concentration of the
compound. To evaluate the minimum concentration required for
the inhibition of bacterial growth; the micro dilution method
was followed.
Minimum inhibitory concentration assay (MIC)
Agar disc diffusion assay of LM-1 to LM-8
The minimum inhibitory concentration of vitamin K3 and all
compounds against P. aeruginosa for S. aureus (in parenthesis) were
shown in Table 7 (Figs. S5 and S6 in ESI ). It can be seen that most
of the compounds showed inhibition only at higher concentration
The compounds of appropriate concentrations were added on to
the disc, dried and sterilized in UV before placing them on the

D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
187
Fig. 6. Illustration of NAHꢁ ꢁ ꢁO (molecules II, III and I, IV) and
p–p stacking interactions (I, III and II, IV) of LM-3.
Fig. 7. Molecules of LM-1 showing ladder like alternating
molecules down c axis(right).
p–p stacking interaction between the neighbouring chains down b-axis(left) and butterfly like arrangement of LM-1
Table 6
Results of agar disc diffusion assay of LM-1 to LM-8 on for Pseudomonas aeruginosa (Staphylococcus aureus).
Compound
Diameter (1
lg/mL)
Of (2
lg/mL)
Clearance (3
lg/mL)
Zone (cm) (5 lg/mL)
Vitamin K3
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
0.2 (0.6)
0.4 (0.5)
0.6 (0.6)
0.5 (0.7)
0.6 (0.6)
0.5 (0.4)
0.4 (0.2)
0.3 (0.3)
0.3 (0.4)
0.8 (0.8)a
0.9 (0.7)
0.8 (0.8)
0.9 (0.9)
0.9 (0.7)
0.8 (0.5)
0.2 (0.5)
0.6 (0.7)
0.5 (0.5)
1.4 (1.0)
1.2 (0.9)
1.0 (0.9)
1.3 (1.0)
1.1 (0.8)
0.9 (0.6)
0.9 (0.6)
0.8 (0.9)
0.7 (0.6)
1.8 (1.2)
1.6 (1.1)
1.4 (1.4)
1.5 (1.2)
1.4 (0.9)
1.2 (0.8)
1.1 (0.9)
1.0 (1.0)
1.2 (0.8)
a
For Staphylococcus aureus.
against P. aeruginosa, however, vitamin K3 showed a good activity
gave the minimum concentration required for the inhibition. From
the data obtained it can be observed that LM-2 and vitamin K3
showed better activity as compared to the other compounds. The
at a minimum concentration of 0.156
mL.
lg/mL and LM-2 at 0.625 lg/
From Table 7, it is clear that LM-2 is much more effective
MIC value for LM-2 was 0.625
lg/mL and 0.3125 lg/mL respec-
against S. aureus, as it shows good activity at a minimum concen-
tively for P. aeruginosa and S. aureus, (Fig. 8) whereas vitamin K3
tration of 0.3125
good antibacterial activity above 0.625
l
g/mL, whereas the other compounds exhibited
g/mL concentration.
showed a minimum concentration of 0.156 lg/mL for P. aeruginosa.
l
The two different assays’s showed that all the compounds and
vitamin K3 were biologically active. The agar disc diffusion assay
showed that the diameter of the clearance zone increased with
increase in concentration of the compounds. While the MIC assay
Mechanism of biological activity
The antitumor and cytotoxic effects of quinonoid drugs
are thought to be mediated through their one-electron or

188
D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
Table 7
Results of minimum inhibitory concentration assay of LM-1 to LM-8 for Pseudomonas aeruginosa and Staphylococcus aureus.
Concentration (
l
g/mL)
Vitamin K3
LM-1
LM-2
LM-3
LM-4
LM-5
LM-6
LM-7
LM-8
0.0024
0.0048
0.0097
0.0195
0.039
0.0781
0.156
0.3125
0.625
1.25
1.4 (1.1)a
1.38 (0.98)
1.2 (0.78)
1.1 (0.63)
0.9 (0.63)
0.7 (0.62)
0.2 (0.65)
0.8 (0.64)
0.6 (0.62)
0.7 (0.20)
0.4
1.4 (0.98)
1.22 (0.88)
1.36 (0.86)
1.1 (0.84)
0.82 (0.78)
0.86 (0.63)
0.85 (0.62)
0.73 (0.61)
0.75 (0.71)
0.15 (0.64)
0.32
1.4 (0.96)
1.36 (0.95)
1.32 (0.97)
1.12 (0.94)
1.1 (0.98)
0.93 (0.96)
0.85 (0.99)
0.76 (0.28)
0.23 (0.35)
0.45 (0.44)
0.55
1.38 (0.97)
1.36 (0.88)
1.33 (0.97)
1.11 (0.94)
1.1 (0.87)
0.98 (0.78)
0.89 (0.63)
0.86 (0.54)
0.84 (0.42
0.15 (0.52)
0.28
1.3 (0.94)
1.32 (0.83)
1.34 (0.96)
1.38 (0.94)
1.36 (0.88)
1.22 (0.83)
1.11 (0.78)
0.96 (0.72)
0.97 (0.51
0.92 (0.31)
0.21
1.4 (0.95)
1.35 (0.85)
1.38 (0.92)
1.37 (0.92)
1.36 (0.89)
1.22 (0.88)
1.1 (0.74)
0.97 (0.68
0.97 (0.71)
0.98 (0.72)
0.62
1.4 (0.96)
1.36 (0.88)
1.37 (0.94)
1.35 (0.92)
1.33 (0.84)
1.1 (0.75)
1.28 (0.62)
0.96 (0.61)
0.97 (0.21)
0.96 (0.6)
0.21
1.4 (0.96)
1.36 (0.84)
1.32 (0.93)
1.36 (0.91)
1.1 (0.86)
0.96 (0.86)
0.97 (0.84)
0.92 (0.73)
0.91 (0.21)
0.96 (0.61)
0.97
1.4 (0.96)
1.36 (0.83)
1.32 (0.91)
1.36 (0.90)
1.1 (0.85)
0.98 (0.85)
0.98 (0.84)
0.92 (0.61)
0.94 (0.26)
0.97 (0.31)
0.97
2.5
5
0.3 (0.32)
0.31 (0.42)
0.46 (0.46)
0.32 (0.34)
0.36 (0.51)
0.21 (0.21)
0.31 (0.51)
0.6 (0.72)
0.6 (0.42)
a
For Staphylococcus aureus.
1.5
1.5
1
LM-2
LM-2
1
0.5
0
0.5
0
Concentraꢀon (μg/mL)
Concentraꢀon (μg/mL)
Fig. 8. MIC plots for LM-2 against Pseudomonas aeruginosa (left) and Staphylococcus aureus(right).
two-electron reduction to semiquinone radicals. Most semiqui-
nones rapidly reduce dioxygen to form superoxide anion radical
and thus regenerate the quinone. Quinones may, therefore, enter
flavoprotein-catalyzed redox cycles with dioxygen which result
in the formation of large amounts of Oꢃ2 ꢀ radical and the oxidation
of reduced pyridine nucleotides. The enzymatic or spontaneous
dismutation of O2ꢃꢀ yields H2O2 and Oꢀ2. Further O2ꢃꢀ and H2O2 can
react together, in a process catalyzed by certain metal ions, to
form even more deleterious oxygen species such as the hydroxyl
radical (OHꢀ) by Fenton reaction and singlet oxygen. The flavopro-
tein-catalyzed redox cycling of quinones in cells would, therefore,
quickly lead to conditions of oxidative stress due to excess of the
superoxide radical. These oxygen intermediates or reactive oxygen
species (ROS) may react directly with DNA or other biomolecules
such as proteins and lipids, which leads to cell damage [21–24].
In in vivo, the flavoprotein NAD(P)H which is a quinone-acceptor
oxidoreductase, catalyzes the two-electron reduction of quinones
to hydroquinones without the formation of semiquinone radical
intermediates, whereas NADPH-cytochrome P-450 reductase and
NADH-ubiquinone oxidoreductase catalyze the one-electron
reduction of quinones to semiquinone radicals. Thus the mecha-
nism of biological activity involves generation of active oxygen
species by redox cycling, intercalation between nucleotides in
the DNA double helix or alkylation of biomolecules.
Conclusions
Synthesis, characterization and evaluation of antibacterial
activity of first eight analogs of n-alkylamino derivatives (LM-1
to LM-8) of vitamin K3 has been discussed in this investigation.
Molecular structure of LM-3 (propyl derivative) has been deter-
mined by single crystal X-ray diffraction and its molecular associ-
ation with neighbouring molecules were investigated in detail.
There were four molecules in asymmetric unit cell of LM-3; they
were named as I, II, III and IV. The four molecules differed by tor-
sion angles and bond angles of the plane of quinonoid ring and
the N-alkyl chain. Molecules I, IV and II, III formed dimer via
NAHꢁ ꢁ ꢁO interaction while there was no molecular association of
molecules I and II similarly III and IV in crystal lattice. The ladders
of all four molecules of LM-3 are observed via CAHꢁ ꢁ ꢁO, NAHꢁ ꢁ ꢁO
and
p–p stacking interactions. The ladders were connected by a
unique CAHꢁ ꢁ ꢁO interaction of n-alkyl group of molecule II to III.
The overall interactions of LM-3 are presented in Fig. 9. Molecules
of LM-1 also formed dimer and further a polymeric chain of dimers
was formed by CAHꢁ ꢁ ꢁO interaction. Neighbouring chains of
dimers showed alternatively p–p stacking of molecules.
Pharmacological potential of all compounds has been evaluated
against two bacterial strains viz P. aeruginosa and S. aureus. All
the compounds showed activity against the two strains under
Fig. 9. Overall interactions of LM-3 molecules.

D. Chadar et al. / Journal of Molecular Structure 1086 (2015) 179–189
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