Turning Down the Complement Amplifier A Claimed Chemical Family Aimed at the Same Target as the First Oral PNH Drug

This application claims a defined family of small molecules that block complement factor B, the protein that starts and sustains the self-reinforcing arm of the complement system. Claim 1 is a compound claim rather than a method of treatment: it defines one chemical skeleton, an indole joined by a single carbon to a piperidine ring, with a tightly specified list of what may hang off each position. The applicant is Shanghai Meiyue Biotech Development, and the diseases named in the later use claims run from a rare blood disorder to a common form of kidney inflammation. This is an Australian divisional of an earlier filing, not a product on the market.

The Problem

Complement is a set of blood proteins that sit around as inactive precursors until something triggers them, after which each one cuts the next in a cascade. Three routes into that cascade are recognised, and the specification is interested in the third. In the alternative pathway, C3b that has settled on a cell surface binds factor B, factor D cuts factor B in two, and the larger fragment joins C3b to form an enzyme that makes more C3b. That enzyme is both a product of the reaction and a component of it, so the output feeds the input. Factor B is the earliest point at which the loop can be shut down.

The specification then works through what goes wrong when the loop runs unchecked. In paroxysmal nocturnal haemoglobinuria, a mutation in a blood stem cell means the red cells it produces lack the anchor that normally holds protective proteins, including CD55 and CD59, on the cell surface. Without those brakes the patient’s own complement destroys their red cells inside the blood vessels. At the time of filing, eculizumab was the only approved drug for the condition, and the specification’s objections to it are practical rather than scientific: it is expensive, it must be given by intravenous infusion, and many patients remain anaemic on treatment and still need transfusions.

The picture for IgA nephropathy is described as worse. There is no specific drug, only blood pressure medicines, glucocorticoids and general immunosuppressants, and the specification points to the STOP-IgAN and TESTING trials as confirming the side effect burden of steroids. It lists a dozen further complement-linked conditions, among them C3 glomerulonephritis, membranous nephropathy, atypical haemolytic uraemic syndrome and geographic atrophy. As at the August 2020 priority date, it records, no small molecule factor B inhibitor was in clinical use anywhere, and it names only three programmes it knew of, from Ionis, Novartis and Achillion.

What This Invention Does

Claim 1 covers a compound, or its racemate, stereoisomer, tautomer, isotopically labelled version or pharmaceutically acceptable salt, having the structure of formula (I-1). The skeleton is an indole with a single carbon bridge from its four position to the nitrogen of a piperidine ring. Around that skeleton the claim fixes most positions and leaves a few open. Four substituent positions must be hydrogen and one may be hydrogen or a halogen. One indole position must carry a small alkyl, cycloalkyl or alkyloxy group, another a nitrile or a small alkyl or cycloalkyl. The piperidine carries an aryl or heteroaryl group, which may itself bear a carboxylic acid or ester.

The genuinely narrow part of the claim, and the part that shows what the applicant was designing around, is the substituent at the four position of the piperidine. Claim 1 requires it to be either an alkyloxy group that itself carries a cycloalkyl or heterocyclyl ring, or one of a short list of ring systems. A plain unsubstituted ethoxy group at that position falls outside the claim. That matters, because iptacopan, the only factor B inhibitor to reach approval, is a 4-ethoxy piperidine built from an indole and a benzoic acid. The worked chemistry here starts from 5-methoxy-7-methyl-1H-indole and 4-bromobenzoic acid, the same two fragments, and then puts something bulkier on the ring position that iptacopan leaves as a simple ether.

The remaining claims follow the usual pharmaceutical sequence. Claims 13 to 15 cover the preparation method, claim 16 a pharmaceutical composition containing a therapeutically effective amount of one of the compounds, and claim 17 adds excipients and combination partners. Claim 18 is a use claim directed to manufacturing a medicament for a disease mediated by activation of the complement alternative pathway, with claim 19 listing the diseases and claim 20 specifying that the primary glomerulonephritis referred to is IgA nephropathy.

The reported testing is a standard cascade: binding to human factor B by surface plasmon resonance and by a competitive fluorescence assay, then functional inhibition by a commercial alternative pathway assay and a rabbit red cell haemolysis test in human serum. In the haemolysis assay the compound of Example 5 gave an IC50 of 87.9 nanomolar against 379.4 for the comparator, which is identified as Example 26c of WO 2015/009616, the Novartis application in which iptacopan was disclosed. Liver microsome stability was run in rat, monkey and human, and there are monkey pharmacokinetic and serum complement activity curves plus a rat arthritis model.

Key Features

• A compound claim, not a treatment claim. Claim 1 secures the molecules themselves, the broadest form of protection available in pharmaceutical chemistry and the hardest to design around.
• One position does the differentiating. The four position of the piperidine must carry a ring or a ring-bearing ether, which is what separates this family from the approved compound built on the same skeleton.
• An acid group on the aryl ring. The aryl substituent may carry a carboxylic acid or ester, the feature that anchors this class of inhibitor in the factor B binding site.
• Composition and use claims travel with it. Compositions, combination products and manufacture of a medicament for alternative pathway diseases are each claimed separately.
• A benchmark drawn from the reference series. Rather than comparing against a placebo, the specification runs a compound taken directly from the Novartis application as its control in every assay.
• A long disease list with kidney disease singled out. Claim 19 names more than fifteen indications, and claim 20 exists solely to pin down IgA nephropathy.

Who Is Behind It

The applicant is Shanghai Meiyue Biotech Development Co., Ltd., a Chinese pharmaceutical developer that keeps little English language presence. Its complement work has been tracked by the trade press, and BioWorld has reported on successive factor B filings from the company, including work done alongside Wuhan Createrna Science and Technology. The three named inventors are Linbo Luan, Yongkai Chen and Chaodong Wang. The Australian filing is handled by Wrays in Perth.

The chain is short. The work was first filed in China as application 202010790872.8 on 7 August 2020, taken international as PCT/CN2021/110859 and published as WO 2022/028527. The Australian national phase became AU 2021323300, and the present application is a divisional of it. The priority country is China.

Why It Matters

The commercial logic of the filing is visible in its own comparator. In December 2023, roughly three years after this work was first filed in China, Novartis received FDA approval for iptacopan as the first oral monotherapy for adults with paroxysmal nocturnal haemoglobinuria. The same drug has since been approved in IgA nephropathy. The proposition this specification was written around, that an oral tablet could displace an infused antibody in a chronic complement disease, has been proven correct by someone else in the interval.

That does not make a second family redundant. Complement diseases are a set rather than a single market, and the conditions in claim 19 differ in how much of the pathway must be shut down and how tolerant they are of infection risk. A compound with different metabolism or tissue distribution can find room, and the specification’s own data are framed in exactly those terms, with the comparator beaten on binding, on functional inhibition and on microsomal stability rather than on any novel mechanism.

Prosecuting a divisional in Australia six years after the Chinese priority date, on a family that already runs through Europe, the United States, Israel and South Africa, is what a company does when it expects the chemistry to be licensed or litigated rather than quietly abandoned.

Related Concepts

• Iptacopan – the approved oral factor B inhibitor used as the comparator throughout the specification.
• Structural analog – the design strategy at work, keeping a proven scaffold and varying one position.
• Ravulizumab – the longer acting successor antibody that shares the infusion burden the specification objects to.
• Geographic atrophy – one of the eye conditions named in the use claims, and an active area of complement drug development.
• Small molecule – the drug class the applicant argues should replace antibody therapy in this field.

---

AU 2026202118 was published in the Australian Official Journal of Patents on 9 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.