Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) is a membrane protein on the endoplasmic reticulum (ER) that transports Ca2+ from the cytosol into the ER. As its function is associated with various biological phenomena, SERCA has been recognized as a promising druggable target. Here, we report the second-strongest SERCA-inhibitory compound known to date, which we isolated from the marine cyanobacterium Leptochromothrix valpauliae and named iezoside (1). The structure of iezoside (1) is fundamentally different from that of any other SERCA inhibitor, and its potency is the strongest among marine natural products (Ki 7.1 nM). In this article, we report our comprehensive analysis of iezoside (1), which covers its isolation, structural characterization supported by density functional theory (DFT) calculations and statistical analysis, total synthesis, and clarification of the mode of action of its potent antiproliferative activity (IC50 6.7 ± 0.4 nM against HeLa cells).

total synthesis, marine cyanobacteria, SERCA inhibitor, iezoside, Leptochromothrix valpaulia

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19	C20	C21	C22	C23	C24	C25	C26	C27	C28	C29	C30
19,2	Me	59.0
19,3	Me	57.4
19	aLRhap	94.5	77.8	82.7	72.5	69.8	18.4
	Subst	143.4	119.6	174.3	50.3	45.0	25.6	22.0	23.4	-	171.4	?	?	32.0	174.9	131.1	128.7	122.0	144.4	49.1	78.9	125.4	139.5	133.1	135.9	22.0	14.2	14.7	15.8	15.3	12.5


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9	H10	H11	H12	H13	H14	H15	H16	H17	H18	H19	H20	H21	H22	H23	H24	H25	H26	H27	H28	H29	H30
19,2	Me	3.36
19,3	Me	3.40
19	aLRhap	4.82	3.56	3.37	3.44	3.60	1.19
	Subst	7.70	7.48	-	5.40	1.85	1.77	0.96	0.96	7.74	-	4.99	1.35	2.86	-	-	6.43	6.19	-	2.46	4.12	5.40	6.23	-	5.52	2.14	0.96	1.91	1.78	1.18	1.72


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9	C10/H10	C11/H11	C12/H12	C13/H13	C14/H14	C15/H15	C16/H16	C17/H17	C18/H18	C19/H19	C20/H20	C21/H21	C22/H22	C23/H23	C24/H24	C25/H25	C26/H26	C27/H27	C28/H28	C29/H29	C30/H30
19,2	Me	59.0/3.36
19,3	Me	57.4/3.40
19	aLRhap	94.5/4.82	77.8/3.56	82.7/3.37	72.5/3.44	69.8/3.60	18.4/1.19
	Subst	143.4/7.70	119.6/7.48		50.3/5.40	45.0/1.85	25.6/1.77	22.0/0.96	23.4/0.96	-/7.74		?/4.99	?/1.35	32.0/2.86			128.7/6.43	122.0/6.19		49.1/2.46	78.9/4.12	125.4/5.40	139.5/6.23		135.9/5.52	22.0/2.14	14.2/0.96	14.7/1.91	15.8/1.78	15.3/1.18	12.5/1.72

The spectrum also has 3 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC/C=C(C)/C=C/[C@@H](O[C@@H]1O[C@@H](C)[C@H](O)[C@@H](OC)[C@H]1OC)[C@H](C)/C(C)=C/C=C(\C)C(=O)N(C)[C@H](C)C(=O)N[C@@H](CC(C)C)c1nccs1

689.96 g/mol (C₃₇H₅₉N₃O₇S)

The accessibility to long, branched and complex glycans containing many 1,2-cis glycosidic linkages with precise structures remains a challenging task in chemical synthesis. Reported here is an efficient, stereoselective and orthogonal one-pot synthesis of a tetradecasaccharide and shorter sequences from Lentinus giganteus polysaccharides with antitumor activities. The synthetic strategy consists of: (1) newly developed merging reagent modulation and remote anchimeric assistance (RMRAA) α-(1→6)-galactosylation in a highly stereoselective manner, (2) DMF-modulated stereoselective α-(1→3)-glucosylation, (3) RMRAA stereoselective α-(1→6)-glucosylation, (4) several orthogonal one-pot glycosylations on the basis of N-phenyltrifluoroacetimidate (PTFAI) glycosylation, Yu glycosylation and ortho-(1-phenylvinyl)benzoate (PVB) glycosylation to streamline oligosaccharide synthesis, and (5) convergent [7 + 7] glycosylation for the final assembly of the target tetradecasaccharide. In particular, this new RMRAA α-galactosylation method has mild reaction conditions, broad substrate scopes and significantly shortened step counts for the heptasaccharide synthesis in comparison with 4,6-di-tert-butylsilyene (DTBS) directed α-galactosylation. Furthermore, DFT calculations shed light on the origins of remote anchimeric assistance effects (3,4-OBz > 3,4-OAc > 4-OBz > 3-OBz) of acyl groups.

synthesis, glycan, antitumor activity, Lentinus giganteus, α-glycosylation

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

Warning = sub-repeat ending at aDGalp: large unit count (6) was reduced to 5
[*]OC[C@H]1O[C@H](OC[C@H]2O[C@H](OC[C@H]3O[C@H](OC[C@H]4O[C@H](OC[C@H]5O[C@H](OC[C@H]6O[C@H](OC[C@H]7O[C@H](OC[C@H]8O[C@H](OC[C@H]9O[C@H]([*])[C@H](O)[C@@H](O)[C@H]9O)[C@H](O)[C@@H](O)[C@H]8O)[C@H](O)[C@@H](O)[C@H]7O)[C@H](O)[C@@H](O)[C@H]6O)[C@H](O)[C@@H](O)[C@H]5O)[C@H](O)[C@@H](O)[C@H]4O)[C@@H](O)[C@@H](O[C@H]4O[C@H](CO[C@H]5O[C@H](CO)[C@@H](O)[C@H](O)[C@H]5O)[C@@H](O)[C@H](O)[C@H]4O)[C@@H]3O)[C@@H](O)[C@@H](O[C@H]3O[C@H](CO)[C@@H](O)[C@H](O)[C@H]3O)[C@@H]2O)[C@@H](O)[C@@H](O[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2O)[C@@H]1O

2107.833 g/mol (C₇₈H₁₃₀R₂O₆₅, R = next and previous repeats, not counted in mol weight)

The accessibility to long, branched and complex glycans containing many 1,2-cis glycosidic linkages with precise structures remains a challenging task in chemical synthesis. Reported here is an efficient, stereoselective and orthogonal one-pot synthesis of a tetradecasaccharide and shorter sequences from Lentinus giganteus polysaccharides with antitumor activities. The synthetic strategy consists of: (1) newly developed merging reagent modulation and remote anchimeric assistance (RMRAA) α-(1→6)-galactosylation in a highly stereoselective manner, (2) DMF-modulated stereoselective α-(1→3)-glucosylation, (3) RMRAA stereoselective α-(1→6)-glucosylation, (4) several orthogonal one-pot glycosylations on the basis of N-phenyltrifluoroacetimidate (PTFAI) glycosylation, Yu glycosylation and ortho-(1-phenylvinyl)benzoate (PVB) glycosylation to streamline oligosaccharide synthesis, and (5) convergent [7 + 7] glycosylation for the final assembly of the target tetradecasaccharide. In particular, this new RMRAA α-galactosylation method has mild reaction conditions, broad substrate scopes and significantly shortened step counts for the heptasaccharide synthesis in comparison with 4,6-di-tert-butylsilyene (DTBS) directed α-galactosylation. Furthermore, DFT calculations shed light on the origins of remote anchimeric assistance effects (3,4-OBz > 3,4-OAc > 4-OBz > 3-OBz) of acyl groups.

synthesis, glycan, antitumor activity, Lentinus giganteus, α-glycosylation

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

Warning = sub-repeat ending at aDGalp: large unit count (6) was reduced to 5
OC[C@H]1O[C@H](OC[C@H]2O[C@H](O[C@@H]3[C@H](O)[C@@H](OC[C@H]4O[C@H](OC[C@H]5O[C@H](OC[C@H]6O[C@H](OC[C@H]7O[C@H](OC[C@H]8O[C@H](OC[C@H]9O[C@H](O)[C@H](O)[C@@H](O)[C@H]9O)[C@H](O)[C@@H](O)[C@H]8O)[C@H](O)[C@@H](O)[C@H]7O)[C@H](O)[C@@H](O)[C@H]6O)[C@H](O)[C@@H](O)[C@H]5O)[C@H](O)[C@@H](O)[C@H]4O)O[C@H](CO[C@H]4O[C@H](CO[C@H]5O[C@H](CO)[C@@H](O)[C@H](O[C@H]6O[C@H](CO)[C@@H](O)[C@H](O)[C@H]6O)[C@@H]5O)[C@@H](O)[C@H](O[C@H]5O[C@H](CO)[C@@H](O)[C@H](O)[C@H]5O)[C@@H]4O)[C@H]3O)[C@H](O)[C@@H](O)[C@@H]2O)[C@H](O)[C@@H](O)[C@@H]1O

2125.848 g/mol (C₇₈H₁₃₂O₆₆)