On April 5, 2018, we entered into an operating lease agreement for 30,175 square feet of office space located in Boston, Massachusetts for our corporate headquarters. The lease commencement date was August 15, 2018 and we took occupancy in September 2018. We are leasing this space under a non-cancelable operating lease with an initial term ending after 123 months and an option to extend the lease for an additional five-year term. We did not include the extension option in our right-of-use asset and lease liability calculation as we do not consider it reasonably certain that we would exercise the option. Under the lease agreement, we received a three-month free rent period, which commenced on August 15, 2018, and a tenant improvement allowance up to $3.8 million. We provided the lessor with a letter of credit to secure our obligations under the lease in the initial amount of $2.4 million, to be reduced to $1.8 million on the third anniversary of the rent commencement date and to $1.2 million on the fifth anniversary of the rent commencement date if we meet certain conditions set forth in the lease at each such time. The letter of credit amount is included in deposits and other assets on the accompanying condensed consolidated balance sheets.

On November 12, 2018, we entered into an operating lease agreement with Ionis to sublease 4,723 square feet of office space located in Carlsbad, California. The lease commenced in March 2018 and the term of the lease is 64 months with a four-month free rent period. There is no extension option for this lease.

We leased office space in a building in Cambridge, Massachusetts under an operating lease that commenced in April 2015 and was subsequently amended and expanded in February 2016 and March 2017. The lease was scheduled to expire in April 2020. We have subsequently terminated the lease effective April 2019.

On May 8, 2019, we entered into an operating lease agreement for office space located in Dublin, Ireland. The lease commenced in May 2019 and the initial term of the lease is 18 months with an extension option for an additional 12 months. We have included the 12-month extension period in our right-of-use asset and lease liability calculation as we consider it reasonably certain that we will exercise the option to extend the lease for an additional 12 months.

Other information related to our operating leases is as follows (dollar amounts in thousands):

	At September 30, 2019
Operating lease right-of-use assets	$	11,300
Operating lease liabilities (1)	$	15,850
Weighted average remaining lease term	9.0 years
Weighted average discount rate		8	%

(1)

Current portion of $1.3 million included in other current liabilities and the difference of $14.6 million included in long-term portion of lease liabilities on our condensed consolidated balance sheet.

Annual maturities of our operating lease liabilities as of September 30, 2019 are as follows (in thousands):

Years ended December 31,	Operating Leases
Remainder of 2019	$	621
2020		2,497
2021		2,502
2022		2,403
2023		2,400
Thereafter		11,961
Total minimum lease payments	$	22,384
Less:
Imputed interest		(6,534	)
Total operating lease liability	$	15,850

Operating lease expense was $0.5 million and $1.6 million for the three and nine months ended September 30, 2019, respectively. In comparison, operating lease expense was $0.8 million and $1.7 million for the same periods in 2018. Cash paid for amounts included in the measurement of lease liabilities for the nine months ended September 30, 2019 was $1.9 million and was included in net cash used in operating activities in our condensed consolidated statement of cash flows.

Purchase commitments include agreements to purchase goods or services that are enforceable and legally binding on us and that specify all significant terms, including fixed or minimum quantities to be purchased, fixed, minimum or variable price provisions, and the approximate timing of the transaction. Such obligations are related principally to inventory purchase orders based on our current manufacturing needs and require significant lead times to be fulfilled by our vendors. Purchase commitments exclude agreements that are cancelable without penalty. As of September 30, 2019 our purchase commitments for the following 12 months were $7.1 million.

In connection with the conclusion of their employment with the Company, Ms. Paula Soteropoulos, our former CEO, Mr. Jeffrey M. Goldberg, our former COO, and Ms. Sarah Boyce, our former President, have entered into Separation Agreements with the Company under which they are entitled to certain severance benefits. As of September 30, 2019, the aggregate severance obligation for these individuals for the following 12 months was $1.8 million and was included in accrued compensation in our condensed consolidated balance sheet. In connection with the conclusion of their employment, we have also entered into Consulting Agreements with Ms. Soteropoulos and Mr. Goldberg pursuant to which they will assist in the transition of their duties and responsibilities. Ms. Soteropoulos and Mr. Goldberg are entitled to receive cash compensation and the continued vesting of any equity awards outstanding as of their dates of separation in consideration for their consulting services.

On September 19, 2019, in connection with his appointment as our interim Chief Executive Officer, Damien McDevitt, Ph.D. entered into (i) a written offer letter with us pursuant to which Dr. McDevitt is entitled to receive certain equity and cash compensation, and (ii) a Severance Benefit Agreement with us pursuant to which Dr. McDevitt is entitled to receive certain severance benefits.

On October 15, 2019, in connection with his appointment as our Chief Commercial Officer, Kyle Jenne entered into a written offer letter with us pursuant to which Mr. Jenne is entitled to receive certain equity and cash compensation. Further, on October 21, 2019, the effective date of Mr. Jenne’s appointment, Mr. Jenne entered into a Severance Benefit Agreement with us pursuant to which he is entitled to receive certain severance benefits.