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Four US companies closed Series B rounds totaling $277 million during the week of April 7-14, 2026. The biggest check went to oncology startup Sidewinder Therapeutics, which pulled in $137 million in an oversubscribed round backed by nine institutional investors. The remaining three deals split evenly between enterprise security and AI-powered legal tech. Compared to earlier-stage activity this week, where six US seed deals totaled $91 million and eight Series A rounds brought in $326.5 million, the B-stage cohort was smaller in deal count but concentrated in high-conviction bets.
Two of the four deals targeted cybersecurity, a sector that continues to attract late-stage capital as enterprises grapple with physical access control and identity governance. Biotech and vertical AI rounded out the mix, with investors backing companies that have moved past proof-of-concept and into clinical pipelines or enterprise sales cycles.
1. Sidewinder Therapeutics Raises $137M for Next-Gen Cancer Drug Conjugates
Deal Overview
- Stage: Series B (oversubscribed)
- Sector: Healthtech / Oncology
- Geography: San Diego, CA
- Round Size: $137 million
- Total Raised: ~$162 million
Investor Profile
The round drew nine investors, led by Frazier Life Sciences, Novartis Venture Fund, and OrbiMed. Goldman Sachs Alternatives, DCVC Bio, Samsara BioCapital, Longwood Fund, Astellas Venture Management, and Alexandria Venture Investments also participated. OrbiMed had been the sole investor in the earlier Series A, and its return signals continued conviction. The presence of Novartis's venture arm and Astellas's investment vehicle brings two major pharma companies into the cap table, a pattern common in oncology deals approaching clinical milestones.
Company and Leadership
Sidewinder Therapeutics was founded in 2023 by Eric Murphy, PhD, who serves as CEO. The company operates under a multi-target license agreement with Lonza's Synaffix ADC technology platform, giving it access to a clinically validated linker and payload system for its drug candidates.
Problem and Opportunity
Standard antibody-drug conjugates target a single protein on cancer cells. That approach works, but it comes with collateral damage to healthy tissue. Sidewinder is building bispecific ADCs that target two proteins simultaneously: an oncogenic driver receptor and an internalizing receptor. The dual-target mechanism is designed to improve tumor selectivity and reduce toxicity, a persistent challenge in the ADC field.
Product and Technology
The company discovers its antibody sequences internally, giving it proprietary binding profiles. Three programs are in the pipeline: SWT012 for bladder cancer (IND filing targeted for late 2026), SWT019 for lung cancer (IND in the first half of 2027), and SWT020 for colorectal cancer (designation nomination in the first half of 2027). The bispecific co-complex targeting mechanism has not yet been commercially validated, which positions Sidewinder as a potential first mover.
Use of Proceeds and Vision
The funds will advance all three bispecific ADC programs into clinical development and support IND filings through 2026 and 2027. Sidewinder is positioning against current-generation ADCs like AstraZeneca and Daiichi Sankyo's Enhertu by claiming a step-change improvement in tumor selectivity through dual-protein targeting.
Market Context
The ADC market exceeds $10 billion and is growing rapidly following the commercial success of Enhertu. Over 100 ADCs are in clinical development globally. Bispecific ADCs represent the next wave, and the oversubscription of this round reflects high investor conviction in the space.
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2. Alcatraz Raises $50M for AI-Powered Physical Access Control
Deal Overview
- Stage: Series B
- Sector: Cybersecurity / Physical Security
- Geography: Cupertino, CA
- Round Size: $50 million
Investor Profile
Investor details for the round were not publicly disclosed at the time of reporting.
Company and Leadership
Alcatraz is a Cupertino-based company building AI-powered physical access control systems for enterprise environments. The company has been developing technology that replaces badge-based and manual security checkpoints with autonomous, AI-driven solutions.
Problem and Opportunity
Enterprise physical security still relies heavily on badge swipes, PIN codes, and manned checkpoints. These systems are easy to circumvent through tailgating, lost credentials, or social engineering. As corporate campuses, data centers, and sensitive facilities grow more complex, the gap between digital security sophistication and physical security infrastructure keeps widening.
Product and Technology
Alcatraz applies AI to physical access control, using computer vision and machine learning to authenticate and manage building entry without traditional credentials. The system is designed to integrate with existing enterprise security stacks rather than rip and replace them.
Use of Proceeds and Vision
The $50 million will fund product expansion and enterprise sales as the company scales its AI-driven access control platform across larger and more complex deployments.
Market Context
The physical access control market is projected to reach $15 billion by 2030. Enterprise buyers increasingly want unified security platforms that bridge the gap between cyber and physical security, creating a tailwind for AI-native entrants.
3. Linx Security Raises $50M for Identity Governance
Deal Overview
- Stage: Series B
- Sector: Cybersecurity / Identity Security
- Geography: New York, NY
- Round Size: $50 million
Investor Profile
Specific investor names were not publicly disclosed at the time of reporting.
Company and Leadership
Linx Security is a New York-based identity security and governance platform focused on helping enterprises manage and secure digital identities at scale.
Problem and Opportunity
Identity has become the primary attack surface for enterprise breaches. As companies adopt more SaaS tools, cloud infrastructure, and distributed workforces, the number of digital identities (human and machine) has exploded. Managing who has access to what, and whether that access is appropriate, is a problem that legacy IAM tools were never built to solve at this scale.
Product and Technology
Linx Security provides an identity governance platform designed to give enterprises visibility and control over their entire identity landscape. The platform addresses the sprawl of permissions, entitlements, and access policies that accumulate across complex IT environments.
Use of Proceeds and Vision
The Series B will fund expansion of the platform's enterprise identity management capabilities and accelerate go-to-market efforts as identity governance becomes a board-level priority for large organizations.
Market Context
The identity governance market is growing as regulatory requirements tighten and identity-based attacks rise. Gartner has flagged identity-first security as a top strategic trend, and incumbents like SailPoint and CyberArk face growing competition from newer entrants tackling the problem with modern architectures.
4. Patlytics Raises $40M for AI Patent Lifecycle Platform
Deal Overview
- Stage: Series B
- Sector: AI / Legal Tech
- Geography: New York, NY
- Round Size: $40 million
- Lead Investor: SignalFire
Investor Profile
SignalFire led the round. The firm is known for its data-driven investment approach and has backed companies across enterprise software and developer tools. SignalFire's involvement suggests the deal was sourced through their quantitative pipeline tracking, which monitors open-source contributions, hiring patterns, and product traction signals.
Company and Leadership
Patlytics is a New York-based company building an AI platform that covers the full patent lifecycle, from search and analysis to prosecution workflows.
Problem and Opportunity
Patent work is one of the most time-intensive areas of legal practice. Searching prior art, analyzing claim scope, and managing prosecution timelines involve massive document volumes and high-stakes decisions. Most of this work still happens in manual or semi-manual workflows, making it expensive and slow.
Product and Technology
Patlytics uses AI to automate patent search, prior art analysis, and prosecution workflows across the entire patent lifecycle. The platform is built to handle the complexity of patent documents, which require domain-specific language understanding that general-purpose LLMs struggle with out of the box.
Use of Proceeds and Vision
The $40 million will go toward product development and scaling the platform's enterprise customer base. Patlytics is building toward becoming the default operating system for patent teams, replacing fragmented toolchains with a single AI-native platform.
Market Context
The global IP software market is valued at roughly $5 billion and growing as patent filing volumes increase worldwide. Legal tech has seen a surge in AI adoption over the past two years, with contract analysis leading the way. Patent lifecycle management is a natural next frontier given the structured, document-heavy nature of the work.
Lessons For Founders
- Oversubscription follows clinical milestones, not hype. Sidewinder's $137M round came with three programs approaching IND filings, not just a thesis deck. Biotech investors at the B stage want to see a pipeline with timelines attached.
- Security keeps attracting B-stage capital. Two of four deals this week targeted security (physical access and identity governance). If your product sits on the critical path of enterprise risk management, you can raise at scale even without flashy AI narratives.
- Vertical AI in boring workflows is a real category. Patlytics is automating patent prosecution, not building a chatbot. The most defensible AI companies at Series B are the ones embedded in domain-specific processes where switching costs compound over time.
- New York is pulling its weight. Two of the four deals this week are headquartered in NYC. For founders outside the Bay Area, the signal is clear: strong enterprise-focused companies can raise Series B rounds without a San Francisco address.
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