Communications
Table 1: Anti-HIV-1 activity of feglymycin and derivatives in MT-4 cells.
All that now remained in the synthesis of the target
[a]
[b]
compound feglymycin (1) was the coupling of the C-terminal
hexamer and N-terminal heptamer fragments, followed by the
cleavage of all protecting groups of the resulting 13-mer
peptide. Removal of the Boc group in 3 led to hydrochloride
35, which was coupled to acid 2 with DEPBT/NaHCO3 in
DMF (Scheme 7). The 13-mer product 36 was obtained after
24 h at 08C and an additional 24 h at room temperature with
42% conversion. Changes in these reaction parameters
resulted in lower yields, in particular when the reaction time
at 08C was shortened. On the other hand, extension of the
coupling time, either at 08C or room temperature, led only to
a significant increase in the formation of by-products. The
separation of protected feglymycin 36 after this step posed a
challenge, because conventional chromatographic purifica-
tion techniques typically resulted in a substantial loss of
material. Only size-exclusion chromatography (sephadex LH-
20, MeOH) afforded almost pure 13-mer 36, the global
deprotection of which by hydrogenolysis (10% Pd/C, H2,
MeOH) gave 1.
Compound
IC50
CC50
Enantiomer
IC50
CC50
[mgmLꢁ1
]
[mgmLꢁ1
]
[mgmLꢁ1
]
[mgmLꢁ1
]
1
2
3
26
1.9
8.9
>100
>4
7.8
0.0037
>100
>100
>100
12.4
>100
>10.0
1’
2’
3’
26’
34’
7.9
8.3
>100
>13
7.7
>100
>100
>100
13.2
34
57.1
AMD3100
[a] IC50: 50% inhibitory concentration, or drug concentration required to
inhibit the virus-induced cytopathic effect (CPE) of HIV-1 NL4.3 in
human MT-4 cells by 50%. [b] CC50: 50% cytotoxic concentration, or
drug concentration required to inhibit the cell growth of MT-4 cells by
50%.
value of the bicyclam fusion inhibitor AMD3100,[20] a CXCR4
coreceptor antagonist, is shown for reference.
The IC50 value of feglymycin (1.0 mm) is comparable to
that of the nucleoside analogue reverse transcriptase inhibitor
(NARTI) zalcitabine (0.95 mm),[21] which was investigated in
previous studies under similar conditions.[19] Besides 1, the N-
terminal heptapeptides 2 and 34 show remarkable activity,
whereas the C-terminal hexamer 3 appears to be ineffective.
As a small molecule, dipeptide 26 also shows interesting anti-
HIV-1 activity; however, it displays cytotoxic effects. A
comparison of the IC50 values (mm) shows that feglymycin is at
least four times more active than all other peptide derivatives
tested. The IC50 values of the enantiomeric compounds 1’, 2’,
and 34’ are comparable to those of the natural derivatives,
which indicates that the absolute configuration of these
substances seems to be of minor importance for their
biological activity. In conclusion, it may be assumed that the
potential pharmacophore is located in the N-terminal region.
Antibacterial tests (see the Supporting Information) showed
exceptional activity of synthetic 1
Enantiomer 1’ was also prepared by the synthetic route
described herein for 1. Synthetic 1 (and 1’) exhibited identical
1
physical properties (Rf, HPLC, H NMR, MS) to those of
natural feglymycin.[1,18]
For the investigation of biological activity, the natural
product and a selection of synthetic intermediates were
chosen for antiviral testing (see the Supporting Information
for complete data). The anti-HIV-1 activity of the compounds
was evaluated in the human MT-4 cell line.[19] Compounds 1
and 2 (also enantiomers 1’ and 2’) and heptapeptide 34 had
activities between 1.9 and 8.9 mgmLꢁ1 and showed no
cytotoxicity at 100 mgmLꢁ1. The other compounds, including
34’, had no significant anti-HIV-1 activity, as their IC50 value
was too close to their toxic concentration (Table 1). The IC50
and a sample of natural 1 against
Staphylococcus aureus (MIC = 1-
4 mgmLꢁ1), contrary to the previ-
ous results of Vꢀrtesy and co-
workers.[1]
In summary, we have de-
scribed a convergent and stereo-
selective synthesis of the highly
acid labile antiviral 13-mer pep-
tide feglymycin (1) and its enan-
tiomer 1’ by the DEPBT-mediated
condensation of repeating frag-
ments. The approach enables fast
access to new potentially interest-
ing derivatives without significant
changes to the reaction protocols.
Future investigations will involve
more detailed studies of biological
activity to shed light on the molec-
ular mode of action of feglymycin.
Scheme 7. Completion of the total synthesis of feglymycin (1): a) 4n HCl/dioxane, 55 min, quantita-
tive; b) DEPBT, NaHCO3, DMF, 08C!RT, 48 h, 42%; c) 10% Pd/C, H2, methanol, room temperature,
5.5 h, 89%.
Received: August 21, 2008
Revised: October 22, 2008
Published online: January 29, 2009
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 1856 –1861